The effect of dietary protein on reproduction in the mare. V. Endocrine changes and conception during the early post partum period

Pregnant Anglo-Arab and Thoroughbred mares (n = 24) were divided randomly according to age and breed into 4 groups of 6 mares each from approximately 6 weeks before their expected foaling date. Diets received by the 4 groups varied in essential amino-acid and total protein contents. Serum progestagen, FSH and LH concentrations were determined from the day of parturition until foal heat and during the 1st oestrous cycle following foal heat. Serum progestagen, FSH and LH concentrations did not differ between the treatment groups. Progestagen concentrations were high (mean = 7.0: 5.2-16.4 ng/ml) at parturition but decreased rapidly within 48 h. As progestagen concentrations decreased LH concentrations increased from Days 3-6 post partum to reach maximum values at, or the day after ovulation. FSH concentrations declined 3-4 d after parturition and increased 2-3 d before ovulation at foal heat. The duration of elevated progestagen concentrations during the luteal phase of the subsequent oestrous cycle affected the interovulatory period. A 12-14 d FSH cyclical releasing pattern occurred. Season/photoperiod affected the resumption of normal oestrous cyclicity during the post partum period. The duration of the 1st oestrous cycle after foal heat in mares fed a low-quality protein diet showed a greater range (13-30 d) compared to mares fed a high-quality protein diet (18-26 d).     

Cell differentiation during early development of Nassarius reticulatus L. (Gastropoda, Prosobranchia). II. Morphological changes of nuclei and nucleoi

Serum LH, FSH and prolactin levels were measured in blood samples which were obtained by decapitation from groups of female, neonatally androgenized female and male Wistar rats at 2-day intervals from birth to maturity. An increase in serum FSH levels was observed between 4 and 24 days of age in both the female and androgenized female groups, while a much later increase, between 28 and 44 days of age, occurred in the males. Serum prolactin contrast, serum LH levels were in general low in all three groups of animals, although very high levels (greater than 7 ng/ml) were recorded in 22 out of 168 females and 8 out of 192 males between 4 and 28 days of age, as well as in adult males; occasional high LH levels were also seen in the androgenized females. The nature of the high serum LH levels was investigated in anaesthetized and unanaesthetized immature females by serial blood sampling using a number of techniques. Unexpectedly, only three out of 58 animals had high LH levels: two of these showed an episodic form of LH release during which levels increased to peak values and then declined within a period of about 30 min. On investigation it was found that general disturbance within the 45 min before decapitation could inhibit high LH levels in females aged between 23 and 30 days.     

Proestrous gonadotropin levels in thyroparathyroidectomized female rats

Intact and TPTx animals showed the expected afternoon increase in serum LH,FSH and prolactin levels. But the afternoon increase in serum LH levels in TPTx rats was less than that observed for intact animals (p less than 0.001). Neither serum prolactin nor FSH levels were altered by TPTx.     

The effect of sulfhydryl reagents on the tityustoxin-induced acetylcholine release in rat brain slices

The effect of breast feeding on serum FSH and LH concentrations was studied in 13 puerperal women. Despite the collateral increase in serum prolactin levels, nursing was not followed by significant changes in serum FSH or LH levels during a 30-min observation period. Our data indicate that nursing has no significant effect on pituitary FSH and LH release.     

The role of maternal thyroid hormones on the development of the brushtail possum, Trichosurus vulpecula

Thyroxine (T4) is a vital hormone for the development of mammals. To determine the role of maternal thyroid hormones on organ development, methimazole, an inhibitor of T4, was first administered via a minipump to 13 mothers with pouch young between days 10 and 80 post partum for 28 days. Three young survived and 10 of the young died at 104.0 +/- 10.8 days post partum (mean, SEM). Methimazole was then administered for 28 days to 6 lactating adult possums with pouch young at day 20 post partum. The effects of this treatment on the maternal plasma concentrations of T4 were monitored and the development of the lung, kidney and brain of the young were examined at day 90 post partum. There was no difference in the morphology of the lung, kidney and brain of pouch young at day 90 post partum whose mothers were treated with methimazole or saline. Thus methimazole administered to lactating possums for a short period early in lactation can cause the demise of the young about day 100 post partum although the cause of death is unknown. It is possible that the development of the central nervous system or some other vital organ has been inhibited, this altered state not being apparent morphologically. Nevertheless the marsupial appears to be similar to the eutherian in its requirement for thyroxine for normal development. However whereas this requirement is apparent during fetal development and around the time of birth in eutherians thyroxine is of importance during pouch development in marsupials.     

Multiple molecular and cellular changes associated with tumour stasis and regression during IL-12 therapy of a murine breast cancer model

The effects of the prolactin inhibiting drug, cabergoline, on pregnant and lactating marsupials were investigated in four species from three diverse families: the tammar wallaby, Macropus eugenii, the quokka, Setonix brachyurus, the brushtail possum, Trichosurus vulpecula, and the fat-tailed dunnart, Sminthopsis crassicaudata. In tammar wallabies, 20 micrograms cabergoline kg-1 injected intramuscularly 1 day before expected birth did not alter the timing of parturition but neonates died within a day of birth, suggesting that the onset of lactation was compromised. During early lactation in tammars (56-69 days post partum), an intramuscular injection transiently retarded growth of the young, although they subsequently survived. This treatment induced reactivation of the quiescent corpus luteum and the blastocyst from diapause, so a new birth occurred 26-27 days later, despite the continued sucking of the young in the pouch. Intramuscular injection during late lactation (166-199 days post partum) apparently suppressed milk secretion since pouch young lost up to 20% of their bodyweight or died within 7 days of treatment. Oral administration of cabergoline had no effect on the growth of the young or on the quiescent corpus luteum and diapausing blastocyst. Quokkas showed similar responses to tammars after treatment in late lactation. Possums and dunnarts were less sensitive to injected cabergoline than the two macropodid species, and possums showed no response to oral administration. The lack of response of these marsupial species to oral cabergoline treatment suggests that accidental ingestion of baits, containing 20 micrograms cabergoline kg-1, used to control introduced eutherian pests such as the red fox, Vulpes vulpes, or the feral cat, Felis cattus, should not affect the reproduction of native marsupials.     

Hypothalamic regulation of pituitary FSH secretion

Temporal changes in plasma LH and FSH concentrations were monitored during the afternoon of proestrus in controls and in rats in which the spontaneous LH/FSH surges were blocked with Nembutal. These values were compared with those obtained following electrochemical stimulation (ECS) of either the medial preoptic area (MPOA) or the dorsal anterior hypothalamic area (DAHA) in similar Nembutal-blocked animals. Whereas MPOA-ECS (60 muA/60 sec) elicited a release of both FSH and LH, similar unilateral stimulation of the DAHA resulted in a pronounced increase in plasma FSH and only a slight elevation in plasma LH. Increasing the amount of DAHA tissue stimulated (100 muA/60 sec) caused a significantly greater release of FSH but not LH. Bilateral DAHA-ECS (60 muA/60 sec) failed to produce a greater release of FSH than that observed after unilateral 100 muA/60 sec ECS but resulted in increased concentrations of LH in plasma. Surgical separation of the MPOA from the DAHA, leaving the preopticotuberal fibers intact, did not alter the spontaneous temporal patterns of discharge of FSH or LH 19-21 days post-operatively, although peak LH concentrations were reduced. Further, unilateral ECS (60 muA/60 sec) of the MPOA in such preparations elicited a release of FSH and LH similar to that observed in intact MPOA-ECS rats. In contrast, unilateral DAHA ECS (60 muA/60 sec) in rats with transected hypothalami, caused no release of LH and an attenuated FSH discharge when compared with intact DAHA-ECS rats (peak valued 189 +/- 8 ng/ml vs 274 +/- 11 ng/ml). These studies suggest the existence of specific cell bodies in the DAHA which can cause selective release of FSH when activated. Coexisting with this system is that level of control which is believed to be responsible for the cyclic discharge of both FSH and LH of which the MPOA is a component part.     

Diagnosis and management of transient ischaemic attacks in accident and emergency

AIM: Are there any changes in hypophyseal and gonadal hormones levels during the naloxone test in the degenerative changes of the seminiferous tubules? MATERIAL AND METHODS: The naloxone test (0.4 mg i.v.) was performed in 13 patients with degenerative changes of the seminiferous tubules. The plasma FSH, LH, prolactin, testosterone and estradiol levels were determined before and 30, 60, 90, 120 minutes after the administration of the drug. RESULTS: In the examined group of patients the plasma FSH, prolactin and estradiol levels were significantly higher, testosterone levels significantly lower and LH levels were in the same range compared with the patients with azoospermia and normal spermatogenesis. The plasma FSH, prolactin and testosterone levels did not change significantly their values during the test. The plasma estradiol levels decreased significantly and plasma LH levels increased significantly during the test. CONCLUSION: Elevated plasma FSH, prolactin and estradiol levels, diminished testosterone levels and the decrease of plasma estradiol levels and the increase plasma LH levels during the naloxone test indicate the degenerative changes of the seminiferous tubules in the cases of azoospermia.     

Hypothalamic-pituitary-ovarian response to clomiphene citrate in women with polycystic ovary syndrome

OBJECTIVE: To examine the hypothalamic-pituitary sites of clomiphene citrate (CC) action in women with polycystic ovarian syndrome (PCOS). DESIGN: Prospective controlled trial. PATIENTS, PARTICIPANTS: Seventeen women with PCOS and 9 normal-cycling women. INTERVENTIONS: Subjects with PCOS received CC, 150 mg/d for 5 days. MAIN OUTCOME MEASURES: Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels and LH pulse characteristics and their response to gonadotropin-releasing hormone (GnRH, 10 micrograms) were examined before and after 3 days of CC in PCOS subjects during a 12-hour frequent sampling study (n = 8). Daily urinary estrone glucuronide and pregnanediol glucuronide levels after CC were compared with concentrations in normal-cycling women through one menstrual cycle. In another nine PCOS subjects, pituitary and ovarian hormonal cyclicity was monitored by daily blood sampling. RESULTS: Thirteen of 17 treated cycles were ovulatory with normal luteal phases. In the ovulatory cycles, serum LH, FSH, estradiol (E2), and estrone levels increased after CC. Luteinizing hormone pulse frequency was unchanged, but LH pulse amplitude increased significantly after CC. Both LH and FSH response to exogenous GnRH was significantly attenuated after CC treatment. In anovulatory cycles, serum LH, FSH, and E2 increased initially and then returned to baseline and remained unchanged for the ensuring 40 days. CONCLUSIONS: Clomiphene citrate-induced ovulation in women with PCOS is accompanied by increased secretion of LH and FSH with enhanced estrogen secretion. The increased LH pulse amplitude after CC, together with decreased pituitary sensitivity to GnRH, suggests a hypothalamic effect.     

Prolonged inhibition of normal ovarian cycles in the rat and cynomolgus monkeys following a single s.c. injection of danazol

In castrated male rats, a single s.c. injection of danazol has been shown to result in an inordinately prolonged inhibition of serum luteinizing hormone (LH) and follicle stimulating hormone (FSH) concentrations. In the present study, we have examined whether the same and similar routes of administration suppresses ovarian function in normally cycling rats and cynomolgus monkeys. Normally cycling female rats received danazol as a single administration either orally, i.m. or s.c. and a separate group also received danazol in silastic capsules. The duration of the dioestrous interval until the next oestrous smear was followed daily and cycle lengths were compared with vehicle-treated groups. Six normally cycling cynomolgus monkeys were followed by daily observation and blood sampling at 2-3 day intervals. After one normal cycle, danazol (200 mg/kg) was administered as a single s.c. injection. Monkeys were followed until the next menses and one cycle thereafter and blood samples were assayed for oestradiol, progesterone and bioactive LH. Oestrous cycle length in vehicle-treated control rats was 4.7 days. A single administration of danazol s.c. at the higher dose prolonged the dioestrous interval to 31.3 days (P <0.001) and a similar prolongation was observed with this high dose when administered i.m. (27.7 days; P <0.001). In normally cycling monkeys, the menstrual cycle length was 30.2 days, but following a single danazol administration, the mean duration to the next menses was prolonged to 117.5 days (P <0.001). In five out of six monkeys, there was a decrease in LH and an absence of normal oestradiol and progesterone patterns. After this prolonged hiatus, a subsequent menstrual cycle was normal in length and endocrine pattern. A single s.c. administration of danazol resulted in a prolonged suppression of ovarian cyclicity in both normally cycling rats and cynomolgus monkeys.     

Mammotrophic activity in rat serum during the oestrous cycle, pregnancy and lactation

The mammotrophic activity of various serum samples was assessed on the mammary gland of pregnant rats, in organ culture. Insulin was added to the medium. Serum samples from virgin rats showed little activity, and variation in mammotrophic activity during the oestrous cycle was slight. During pregnancy a significant increase in proliferative activity was not seen during the first week, but around day 8-9 mammotrophic activity increased sharply. The activity showed maxima around days 12 and 19. A decrease in the activity between these maxima was not consistently observed. Mammotrophic activity was still present in sera collected during parturition, and 30 min after parturition. It had disappeared completely within 24 h. The mammotrophic factor detectable by organ culture in the serum of pregnant rats could be rat chorionic mammotrophin. Activity in the serum on day 0 and 1 of lactation was comparable to that of virgin rats, but some activity appeared on day 2. High actvities were foound frequently around day 4 to 6 of lactation. On other days the activity showed fluctuations without a definite pattern. Litter size was of minor importance but the combination of a larger litter size and fasting-overnight seemed to suppress the presence of mammotrophic activity in the serum. Nursing was important: after weaning the activity has disappeared, while renewed nursing after weaning resulted in the appearance of high levels of activity. The mitotic activity obtained with lactating rat serum in the culture was suppressed by addition of rabbit anti-rat prolactin serum to the medium. This suggests that the main mammotrophic factor detectable by organ culture in the serum of lactating rats, is prolactin.     

Effect of infarct artery patency on prognosis after acute myocardial infarction. The Survival and Ventricular Enlargement Investigators

In this study, adult male rats were injected intraperitoneally with a single dose of serotonin (5-hydroxytryptamine, 5HT; 10 mg kg-1 bodyweight) for 2 h or 18 h, or daily with graded doses of 5HT (0.1-10 mg kg-1) for four days before being killed. Serum and testicular interstitial fluid (IF) concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone and immunoreactive-inhibin were measured by radioimmunoassay, and one testis was removed for histological examination. At 2 h after a single injection, 5HT caused a significant inhibition of serum concentrations of LH and inhibin, recovered IF volume and intratesticular testosterone concentrations; testis weight and serum concentrations of testosterone and FSH were unaffected. At 18 h after injection, all parameters had returned to normal, with the exception of intratesticular testosterone concentration which remained lower than normal. The lowest 5HT dose (0.1 mg kg-1) had no effect on any parameter following four daily injections. At a dose of 1.0 mg kg-1 5HT, there was a four-fold increase in the concentration of serum LH, but testis weight, recovered IF volume, testosterone and inhibin concentrations and serum concentrations of FSH were not significantly affected. At the highest dose of 5HT (10 mg kg-1) after four daily injections, testis weight decreased, and IF volume increased nearly three-fold. Testis concentrations of inhibin and serum testosterone were reduced, whereas serum concentrations of both LH and FSH were elevated; intratesticular testosterone concentrations did not differ from controls. Only at the highest dose of 5HT was disruption to the seminiferous epithelium observed, with focal damage ranging in severity from increased degeneration of spermatogenic cell profiles, to complete loss of the germinal epithelium; however, many tubule profiles displayed completely normal spermatogenesis. The acute IF volume reduction and spermatogenic disruption in 5HT-treated rats were consistent with localized ischaemia due to constriction of the testicular arterial supply. The eventual increase in IF volume observed after 5HT treatment appeared to be secondary to the loss of germ cells. Although 5HT also inhibited pituitary LH release and Leydig cell steroidogenesis, these effects appeared to play only a minor role in the induction of spermatogenic damage.     

Differences of the effects of testosterone propionate on the production of LH and FSH

The effects of testosterone propionate (1 mg/day) on the synthesis and circulating levels of FSH and LH were studied in normal adult male rats. The pituitary and serum gonadotrophins were measured by double antibody radioimmunoassay. The de novo synthesis of gonadotrophins was assessed by the rate of in vitro incorporation of [3H]leucine into the immunoprecipitable FSH and LH. After 4 days of treatment with testosterone propionate the circulating LH levels dropped significantly, while FSH remained unchanged. Pituitary LH content and concentration declined significantly after 1 day, and incorporation of [3H]leucine into the immunoprecipitable LH became undetectable 4 days after initiation of treatment. Pituitary FSH content and concentration showed a significant increase after the 4th day of treatment. A slight tendency towards increased incorporation of [3H]leucine into FSH was observed throughout the treatment period, although it was statistically not significant. The data provide direct evidence for a differential effect of TP on FSH and LH production by the pituitary and show that the decrease in the pituitary and plasma levels of LH in testosterone treated rats is due to the decrease in LH synthesis.     

On the dynamics between gonadotrophin surge-inhibiting factor and gonadotrophin releasing hormone (GnRH): role of self-priming and desensitization in the luteinizing hormone response to GnRH after follicle stimulating hormone treatment

The effects were studied of follicle stimulating hormone (FSH)-induced production of gonadotrophin surge-inhibiting factor (GnSIF) on three phases of the pituitary responsiveness to gonadotrophin releasing hormone (GnRH): the unprimed, primed and desensitized phases. Rats were injected with FSH on two occasions during the oestrous cycle. Spontaneous luteinizing hormone (LH) surges were measured as well as GnRH-induced LH surges on the day of pro-oestrus during infusions with 100-4000 pmol GnRH/rat/10 h, in phenobarbital blocked rats. The spontaneous LH surges were attenuated or completely inhibited by the FSH treatment. FSH suppresses and prolongs the unprimed LH response and delays GnRH self-priming, especially during infusions with low concentrations of GnRH. This treatment does not affect the total LH response (area under curve) to the highest concentrations of GnRH and after ovariectomy. On the other hand, this response is suppressed during infusions with the lower concentrations of GnRH. Hence, FSH, via GnSIF, delays maximal priming of the LH response to GnRH, whereas the suppression of LH release is a consequence of the GnRH-induced progressed state of desensitization. The inconsistent effects of FSH on the mid-cycle LH surges are explained as a result of the interaction between the relative strengths of GnRH and GnSIF.     

The rate constant K37 in complement fixation tests: kinetic studies on the influenza virus-immune complex model (author''s transl)

Diurnal variations in serum hormone levels during 2 different stages of prepubertal development were investigated in male and female rats. Groups of 13 to 18 and 25 to 30 day old male and female rats were decapitated at 4-hour by intervals during a period of 24 h. Their blood was collected and hormones were measured by radio-immunoassay. FSH levels were constantly high in 13 to 18, but low in 25 to 30 day old females. FSH was low in younger males, and significantly higher but without diurnal fluctuations in the older males. Serum LH was low in approximately 40% of the 13 to 18 day old females, while 40% had moderately high levels, and the remaining females extremely high levels of the hormone. Most of the extremely high LH peaks were found at 15.00 h and some at 03.00 h. Older females and males of both age groups had constantly low serum LH levels. Serum oestradiol was high in males and females during days 13 to 18, but it was lower in the 25 to 30 day old animals. In the young females prolactin was slightly elevated between 15.00 h and 19.00 h, while in the males the serum prolactin fluctuations were not significant. Serum testosterone was low in females at all times. The 13 to 18 day old males had higher testosterone levels than the 25 to 30 day old males. Both groups showed slight, but insignificant fluctuations in serum testosterone.     

Influences of deviations of thyroid functions on the effects of MAOI in rats--changes of 5-HT, 5-HIAA and norepinephrine contents and tyramine uptake by the brain and fluctuation of the rectal temperature]

The drug 6-hydroxydopamine (6-OHDA) has been reported to reduce hypothalamic norepinephrine (NE) content after administration into the lateral ventricle without altering the dopamine content of tubero-infundibular neurons. Serum prolactin levels in male rats injected with 2 X 250 mug 6-OHDA were significantly higher than in untreated control rats. Intraventricular injection of male rats with artificial cerebrospinal fluid resulted in elevated mean prolactin levels similar to those observed in 6-OHDA-treated animals. Further experimentation on animals decapitated at different times after removal from the animal quarters, indicates that prolcatin levels in 6-OHDA-treated rats are continuously elevated whereas they rise from basal levels to extremely high levels in CSF-treated rats, thus resulting in similar mean values. The CSF-treated controls ate hypersensitive to the stress of being removed from their normal environment. Such an effect was not observed in 6-OHDA-treated nor in untreated, and thus stress-inexperienced rats. In a long term study, serum prolactin and luteinizing hormone (LH) levels were followed over a period of 71 days after 6-OHDA treatment. Prolactin levels increased within one day after treatment and stayed at a high level for 15 days. Subnormal prolactin values were measured 37 days after 6-OHDA treatment. Serum LH levels were below normal 3 h and one day and were increased 37 and 71 days after 6-OHDA treatment. These results suggest that NE is important in the transmission of stressful stimuli to hypothalamic prolactin regulating centers. They further suggest functional recovery of LH and prolactin regulating mechanisms after 6-OHDA treatment.     

TRH stimulation as an attempt at demonstration of the induction and involution of prolactin-secreting pituitary cells in pregnancy and puerperium and in pathological hyperprolactinemia

The present paper discusses the relationship between functional hypertrophia or hyperplasia of the prolactin secreting cells in the pituitary and actual pituitary prolactin reserves in pregnant and post partum women. 35 randomly selected post partum patients from the 3rd to 12th day p.p. and 14 women in their 11th to 14th weeks of pregnancy volunteered to undergo a standard TRH-test. The control group consisted of 60 normoprolactinemic patients. Eleven pathologically hyperprolactinemic patients were compared to the normoprolactinemic and physiologically hyperprolactinemic groups. In all cases, plasma prolactin showed a linear decrease from the 3rd to 12th days post partum. The TRH induced increase became correspondingly greater as the basal prolactin levels decreased, i.e. an inverse relationship between these two parameters was seen. The TRH-induced increase was also always greater than the increase caused by suckling. A connection between prolactin and parity was not found. The inverse relationship between basal prolactin levels and the actual reserves which could be released by TRH stimulation can be explained in that there are two regulatory systems for prolactin. The estrogens stimulate basal prolactin and inhibit prolactin reserves. The actual prolactin reserve is, on the one hand, directly dependent on the degree of endogenous neurohormonal stimulation and, on the other hand, indirectly dependent on the endogenous estrogens through a feedback mechanism. The TRH-stimulation test is not suitable for determining a functional hypertrophia or hyperplasia of lactotropic pituitary cells.     

Developmental expression of defensive responses during exposure to conspecific adults in preweanling rats (Rattus norvegicus).

Examined preweanling rats' (Rattus norvegicus) expression of ultrasounds and secretion of adrenocorticotrophic hormone (ACTH) when exposed to unfamiliar adult male rats or to their mothers. Pups at 7 days of age produced similar levels of ultrasonic vocalization near both unfamiliar males and mothers. However, these pups could discriminate familiar from unfamiliar adults because ACTH was significantly higher in pups near adult males than in those near mothers. At 14 days of age, pups avoided adult males but not their mothers; therefore, adult males represented a significant threat. Importantly, 14-day-old rats significantly reduced ultrasound production only when near adult males. Pups at 21 days of age no longer emitted ultrasounds when socially isolated or when near conspecific adults. In addition, 14- and 21-day-old rats produced similar elevated ACTH levels across stimulus conditions. Results show significant changes in preweanling rats' responses to conspecific adults. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Structure of the Golgi apparatus in stimulated and nonstimulated acinar cells of mammary glands of the rat

The structural features of the Golgi apparatus of acinar cells of mammary glands were examined with the electron microscope in 3 groups of rats: (1) in lactating female animals at 8 days postpartum, which served as controls; (2) in female rats sacrificed at various intervals from 2 to 30 hours following separation from their 8-day old pups; and (3) in females separated from their 8-day-old pups for a period of 12 hours and returned to their litters for durations of 1, 2, 4, and 8 hours. In animals of group 2, the Golgi stacks remained identical to that of controls between 2 and 8 hours. At 12 hours and later, the Golgi stacks decreased progressively in size, but the number of elements composing the stacks remained similar to that of lactating females and all contained casein submicelles. At 24 and 30 hours, typical secretory granules containing casein micelles disappeared from the trans aspect of the stacks. The earliest and most striking changes observed in the Golgi apparatus of the rats of group 2 took place at 12 hours. At this time, the prosecretory and secretory granules decreased considerably in volume and lost most of their electron-lucent content. This indicated that the delivery of small molecules, i.e., lactose and H2O, to these structures was soon altered following arrest of the sucking stimulus. In animals of group 3, the size of prosecretory and secretory granules and the amount of their electron-lucent content reverted to normal at 4 hours. Thus the influx of lactose and H2O into these structures appears to be rapidly restored after returning the pups to their mothers. The decrease in size of the Golgi stacks noted at 12, 18, and 24 hours following arrest of lactation (group 2), was accompanied by an increase in number of small vesicles that formed clusters next to the Golgi stacks and in "wells." Thus in these regressing Golgi stacks, many of the associated small vesicles appear to arise by vesiculation of the saccules.     

Interactions of the light-dark cycle, adrenal glands and time of steroid administration in determining the temporal sequence of LH and prolactin release in female rats

The purpose of this study was to determine the effects of the light-dark cycle, adrenal glands and steroid treatment schedule on LH and prolactin release in rats. Rats maintained in either a 14 h light: 10 h dark schedule (LD) or constant illumination (LL) were ovariectomized (Ovx) or ovariectomized and adrenalectomized (Ovx-Adx). Three weeks later at 1000 h, animals received a SC injection of estradiol benzoate (EB 10 mug/100 g BW) or oil. Three days after EB administration, rats were given a 2 mg injection of progesterone (P) or oil at either 0200, 0500, or 0900 h, and were sequentially bled at four-hour intervals until 1700 h. P administered at all three times increased the amplitude of the plasma LH surge and advanced it, though by no more than 4 hours, in LD. In LL, P was more effective in advancing the time of LH release, although peak plasma LH levels were considerably less than those observed in LD. Adrenalectomy increased the sensitivity of Ovx rats to the effects of EB and P on LH release. P administration at either 0200, 0500 or 0900 h advanced prolactin release in EB-primed Ovx and Ovx-Adx in LL and LD, but only in LL did P increase the amplitude of the plasma prolactin surge. The lighting conditions did not alter the effectiveness of P in advancing prolactin release. Our study demonstrates that the light-dark cycle and adrenal steroids interact to synchronize the timing of LH release in rats, but the regulatory mechanism controlling prolactin release is less strictly cued to these environmental factors.