Nature of the Thermal pretransition of synthetic phospholipids: dimyristolyl- and dipalmitoyllecithin

The hydrated synthetic lecithins, dimyristoyl and dipalmitoyllecithins, undergo two thermal transitions, a broad low enthalpy "pretransition" prior to the sharp first-order "chain-melting" transition. Both phospholipids exhibit the same temperature-dependent structural changes associated with the thermal pretransition. At low temperatures, below the pretransition, a one-dimensional lamellar lattice is observed. The hydrocarbon chains are fully extended and tilted with respect to the plane of the lipid bilayer. The hydrocarbon chain packing displays a temperature dependence and the angle of tilt of the hydrocarbon chains decreases with increasing temperature, reaching a minimum value of 30 degrees at the pretransition temperature of both lecithins. The pretransition is associated with a structural transformation from a one-dimensional lamellar to a two-dimensional monoclinic lattice consisting of lipid lamellae distorted by a periodic ripple. The hydrocarbon chains remain tilted in the temperature range intermediate between the pretransition and chain-melting transition. The cell parameters of this two-dimensional lattice exhibit a compositional dependence. The a parameter (proportional to the lamellar repeat distance) increases with increasing water content, while the b parameter (a measure of the ripple periodicity) decreases with increasing water content. At the chain-melting transition, the hydrocarbon chains of the phospholipid melt and assume a liquid-like conformation and the lattice reverts to one-dimensional lamellar. These structural changes observed for dimyristoyl- and dipalmitoyllecithins may be a common feature of all synthetic lecithins exhibiting a thermal pretransition. The appearance of the pretransition and accompanying two-dimensional may arise from specific interactions between the choline moiety of the polar head group and the structured water matrix surrounding it.     

Frequency response analysis of the diaphragm in vivo

Frequency response analysis was used to determine the dynamic response characteristics of cat diaphragm under isovolumetric conditions at functional residual capacity (FRC) and at lung volumes above and below FRC. In apneic cats, sinusoidally modulated pulse rate patterns were applied to both phrenic nerves. Modulation frequencies over the range of 0.05-4 Hz were used. Amplitude ratio vs. frequency plots obtained at FRC for intratracheal, intraesophageal, and intragastric pressures were essentially flat at low frequencies but decreased at higher frequencies. Intratracheal and intraesophageal pressure responses were altered by changes in resting lung volume while intragastric pressure was not. The amplitude ratio was decreased at lung volumes above FRC but increased at volumes below FRC. Thus, lung volume significantly affected the input-output relations between phrenic nerve input and diaphragm muscle output. In all preparations studied, significant phase lags were present throughout the entire modulation frequency range. However, in contrast to the effect of lung volume on amplitude ratio, phase lag was not dependent on changes in lung volume.     

DNA synthesis of human, mouse, and rat mammary carcinomas in vitro: influence of insulin and prolactin

Carcinomatous mammary tissues, derived from six spontaneously arising mouse mammary tumors, six DMBA-induced rat mammary tumors, and 26 biopsy specimens of human breast tumors, were processed into slices and each tumor was inidvidually cultured for two days in Medium 199. The influence of bovine insulin (5.0 mug/ml) and ovine prolactin (10.0 mug/ml) on H3-thymidine incorporation into DNA was determined on the cultured tumor slices. Insulin consistenly (p less than 0.05-0.01) increased the incorporation of H3-thymidine into DNA of the organ cultures of mouse, rat, and human mammary carcinoma slices. The stimulatory effect of insulin was quantitatively more prominent in the mouse tumor slices than in the rat or human slices. The addition of prolaction to the insulin-containing culture medium further increased significantly (p less than 0.001) the incorporation of H3-thymidine into DNA of rat mammary carcinoma slices but had no significant effect on cultures of either mouse or human mammary carcinomas. The addition of prolactin to insulin and hydrocortisone-enriched medium containing slices of 20 individually cultured human breast carcinomas did not significantly influence the mean incorporation of H3-thymidine into DNA. However, a very small fraction (approximately equal to 15%) of these human breast carcinomas responded to prolactin by increasing the incorporation of H3-thymidine into DNA to a degree quantitatively comparable to the prolactin-sensitive, DMBA-induced rat mammary carcinoma. These results suggest that a very small fraction of human breast malignancies may respond to the growth-stimulatory effects of prolactin, but that the vast majority mimic more closely the prolactin-independent mouse mammary carcinoma.     

Studies on the peripheral blood and the in vitro response of peripheral blood lymphocytes to common mitogens in Macaca speciosa

In a longitudinal study on 13 adult female stumptailed macaques, Macaca speciosa, peripheral blood samples were analyzed hematologically and the in vitro response of the lymphocytes to the common mitogens concanavalin A, phytohemagglutinin and pokeweed mitogen were investigated. The results showed that the total leukocyte and differential counts in each animal remained quite stable throughout the 3-month experiment. The responses in culture to the mitogens showed that there were differences in the stimulation obtained by each mitogen and that the animals may be placed into high, medium and low groups based on differences in their level of response.     

Intensive care of the pregnant diabetic

Over the last 2 years at Metropolitan Hospital Medical Center 245 diabetic women have been seen on the obstetric service. This complication of pregnancy comprises 7.9 per cent of 3,076 deliveries, resulting in an over-all uncorrected perinatal mortality rate of 2.9 per cent. We believe that early detection and strict rigid control of diabetes is the key to improved perinatal outcome. This article presents the classification, diagnosis, and management which have led to these results.     

The rare problem of late recurrence in neuroblastoma

Two-year disease-free survival is considered highly predictive of therapeutic success with neuroblastoma and death from neuroblastoma greater than 5 years after diagnosis is a rare event. We report of an unusual case of death from neuroblastoma 20 years after diagnosis; a literature review and discussion of this rare phenomenon of late recurrence is also included. Five additional cases of late recurrence, defined as greater than 5 years after diagnosis, were found in the literature with adequate detail to be reviewed. Advanced disease was present at diagnosis in five of six cases; three of six had disseminated disease. No age or sex differences were noted. A peculiar tencency for recurrence during the teenage years, preceded by a long disease-free interval, was also present in all cases, perhaps a reflection of maturational alterations in the immune system or hormonal changes that previously had suppressed extensive disease. This phenomenon of late recurrence in neuroblastoma, albeit rare, adds another facet to the clinical behavior of an enigmatic and therapeutically unyielding childhood tumor.     

Persistence of thromboxane A2-like material and platelet release-inducing activity in plasma

During the incubation of arachidonic acid with platelet-rich plasma, a persistent activity appeared that caused the release of [14C]5-hydroxytryptamine from indomethacin-treated platelets. By the time-course of its appearance and disappearance, this release-inducing activity could be dissociated from prostaglandin endoperoxides and associated with thromboxane A2-like material. This material persists in plasma because of its continued production and increased stability.