Circadian responsiveness of the hypothalamic-pituitary axis

Five healthy men 25-38 years old were subjected to simultaneous composite intravenous stimulation tests of insulin hypoglycemia (0.1 U/kg), thyrotropin-releasing hormone (TRH, 100 mug), and luteinizing hormone-releasing hormone (LHRH, 50 mug) at weekly intervals to study the circadian responsiveness of the hypothalamic-adenohypophyseal axis at 0600, 1200, 1800, and 0000 hours. Blood sugar (BS), LH, follicle-stimulating hormone, TSH, prolactin, cortisol (C), growth hormone, and testosterone (T) levels were estimated before and after the administration of drugs. Comparisons were made between basal and delta values (difference between basal and peak or nadir levels) at different tests. Significant circadian variations in BS, GH, C, and, to a lesser extent PRL, responses were observed 0600 h basal and delta BS values were the lowest, delta BS was highest at 0000 h accompanied by maximal hypoglycemic symptoms; the delta values of both C and GH were significantly higher at 0600 h and 0000 h; highest mean delta PRL was observed at 0600; at 1800 h the basal plasma PRL level was maximum but the delta PRL was lowest. Plasma TSH, LH, and FSH responses did not show significant circadian variations. These results suggest that circadian variations are evident when stimuli act through central or hypothalamic mechanisms; however, direct stimulation of the adenohypophysis resulted in indentical responses at different periods tested.     

A simple method for the assay of eight steroids in small volumes of plasma

A simple method is described for the simultaneous radioligand assay of four delta5-3beta-hydroxysteroids adjacent to one another on the biosynthetic pathway (pregnenolone [1], 17alpha-hydroxypregnenolone, dehydroepiandrosterone and 5-androsterone-3beta, 17beta-diol), and their four delta4-3keto products (progesterone, 17alpha-hydroxyprogesterone, 4-androstene-3, 17-dione and testosterone). Two plasma aliquots are extracted and fractionated each for four steroids and individual corrections are made for losses. For fractionation, maximum use is made of the high resolution and reproducibility of celite minicolumns, using propylene glycol as stationary phase, and a discontinuous gradient of ethyl acetate in iso-octane as mobile phase. The fractions are then assayed in the appropriate radioligand end-assay system. Each assay was finally validated by demonstrating coincidence of peaks of immuno- and radioactive steroid in extracts of female plasma. Results in pre-pubertal girls and women in the follicular phase of the menstrual cycle suggest that the major change in adrenal steroid production at puberty may be an increase in 17, 20-desmolase activity. There appears to be little reversal of this change in adrenal function after ovariectomy.     

Relationship between cell size, plasma cholesterol and rat adipocyte cholesterol storage

Organotypic cultures of newborn hamster choroid plexus were inoculated with equal titre doses of newly isolated or hamster adapted strains of mumps virus. The ultrastructure of virus replication in choroid epithelial cells of the cultures was compared. No qualitative differences were observed; however, the adapted strain produced significantly greater numbers of virions and earlier destruction of the cultures. These findings are consistent with previous in vivo observations of the ultrastructure of the replication of these strains in the newborn hamster central nervous system. This in vitro study leads further support to the hypothesis that differences in the in vivo biological effects of the virus strains are primarily the result of virus-cell rather than virus-host interactions.     

Radiation incidents with a cobalt-60 teletherapy unit

To separate fact from fiction regarding the susceptibility of women athletes to injury, three surveys were conducted. The initial data were collected from the athletic departments of collegiate institutions, and the final material was assembled from certified athletic trainers at these institutions, plus an extensive computer search of applicable publications. The collected statistical data were tabulated, and a written commentary was evaluated by the authors. It was established that injuries sustained by female athletes, aside from those related to different biological structures, were essentially no different than those of men, nor are well-trained women athletes more prone to injury. Ankle and knee injuries are most frequent, and women sustain many contusions, sprains, and shin splints. It is anticipated that the overall number of injuries will decrease as better coaches and trainers become available to women athletes.     

Analysis of three amphibian populations with quarter-century long time-series

Amphibians are in decline in many parts of the world. Long tme-series of amphibian populations are necessary to distinguish declines from the often strong fluctuations observed in natural populations. Time-series may also help to understand the causes of these declines. We analysed 23-28-year long time-series of the frog Rana temporaria. Only one of the three studied populations showed a negative trend which was probably caused by the introduction of fish. Two populations appeared to be density regulated. Rainfall had no obvious effect on the population fluctuations. Whereas long-term studies of amphibian populations are valuable to document population declines, most are too short to reveal those factors that govern population dynamics or cause amphibian populations to decline.     

Hypolipidemic activity of boronated nucleosides and nucleotides in rodents

Base-boronated nucleoside and phosphate-boronated nucleotides were potent hypolipidemic agents in rodents, lowering both serum cholesterol and triglyceride levels. Rat VLDL and LDL cholesterol levels were generally reduced and HDL cholesterol levels were significantly elevated after 14 days dosing at 8 mg/kg/day. Tissue cholesterol, triglyceride and phospholipid levels were reduced by selected derivatives. Increased fecal excretion of lipids did not appear to be a mechanism by which these derivatives lowered serum lipids in rodents. Rather, the agents suppressed appetite and reduced the activities of rate-limiting enzymes for de novo lipid synthesis, specifically cytoplasmic acetyl CoA synthetase, squalene synthetase, and phosphatidylate phosphohydrolase with IC50 values of approximately 10(-5) m.     

Effects of SR 141716A after acute or chronic cannabinoid administration in dogs

This study was undertaken to investigate the effects induced by the systemic administration of RB 101 [N-[(R,S)-2-benzyl-3[(S)(2-amino-4-methylthio)butyl dithio]-1-oxoprpyl]-L-phenylalanine benzyl ester], a mixed inhibitor of the enkephalin catabolism able to cross the blood-brain barrier, in antinociception produced by adrenal medullary tissue transplanted in the rat spinal subarachnoid space. For this purpose, the antinociceptive responses induced by intravenous (i.v.) administration of RB 101 were evaluated in the tail-flick in rats transplanted 28 and 56 days before the test. Systemic administration of RB 101 induced antinociceptive effects in sham-operated rats, as previously reported. RB 101 also enhanced significantly the antinociception produced by the autotransplant 28 and 56 days after surgery. The antinociceptive responses of RB 101 in both sham-operated and autotransplanted rats were blocked by naloxone, but were not modified by the noradrenergic antagonist, phentolamine, suggesting a selective involvement of opioid mechanisms. The present results indicate that the inhibitors of enkephalin catabolism enhance the antinociception induced by adrenal medullary transplants.