M. X. Zarrow

Diurnal rhythm in plasma corticosterone and lack of diurnal rhythm in plasma compound F-like material in the rat.

Summary Concentration of corticosterone in blood of the rat varied as a function of time of day. Highest levels of corticosterone were found between 2 and 3 p.m., and 9 and 10 p.m. There was no diurnal variation in concentration of an unknown component of adrenal origin found in blood. These data supply additional evidence for presence of a diurnal rhythm in secretory activity of the adrenal cortex and support the concept that corticosterone is the glucocorticoid of physiological significance in the rat. Samples of corticosterone and 17-hydroxycorti-costerone were supplied through courtesy of Merck, Rahway, N. J., and Upjohn Co., Kalamazoo, Michigan.

Steroids and carbohydrate metabolism in the domestic bird.

Summary The effects of a series of steroids on the carbohydrate metabolism of the bird were studied using blood glucose and liver glycogen as endpoints. The highly active compounds in the hyperglycemic reaction were hydrocortisone and corticosterone and the active compounds in the liver glycogen test were the above two plus 11-dehydrocorti-costerone. Cortisone was inactive in both tests and 11-desoxycorticosterone acetate was tested only in the hyperglycemia reaction and was inactive. If hydrocortisone is assigned an activity of 100 in the glycogen test, then corticosterone shows an activity of 12.5 and 11-dehydrocorticosterone an activity of 1. In direct contrast to the mammal, cortisone is inactive in the bird. Testosterone appears to lower blood glucose but this apparently is a result of an increase in red blood cell number rather than an absolute drop in glucose present in the blood. Stilboestrol had no effect on blood glucose levels.

Maternal Behavior in the Rabbit Critical Period for Nest Building Following Castration During Pregnancy.

Summary A critical period of exposure to certain hormones appears to be necessary for maternal-nest building since no nest building occurs in animals castrated before day 14 of gestation. It appears that ovarian steroids must act for a period of 16 or 17 days for the occurrence of maternal-nest building.

Blockade of ovulation in the hen with adrenolytic and parasympatholytic drugs.

Summary and Conclusions Both atropine and SKF-501 block the normal occurring ovulation and the progesterone-induced ovulation in the hen. It is suggested that a neural link must be present in the mechanism regulating ovulation in the hen. This link may be similar to that postulated for the rat and the rabbit.

Seasonal variation in thyroid gland activity in deermice.

Summary Thyroid gland activity as measured by percent colloid, cell height, I131 uptake and thyroxine secretion rates was studied in 2 subspecies of male deermice (P. m. bairdii and P. m. grocilis) during spring, summer, fall and winter. A seasonal difference in activity of the thyroid gland was noted in both subspecies. However, time of maximum and minimum activity also varies in the 2 subspecies. Thyroid cell height and TSR are at a maximum during December-March and a minimum in October for bairdii, and are at a maximum during October-December and a minimum during March-July for gracilis. Radioiodine uptake by the thyroid glands of both subspecies is high during July and December and low during March and October. With the exception of the October period, the thyroid gland of bairdii is more active throughout the year than the thyroid of gracilis. A lack of agreement with all parameters of thyroid activity utilized was noted.

Postnatal Changes in the Pituitary-Adrenal Axis of the Rat

Summary The adrenal gland of the 2-day old responds to unilateral adrenalectomy by a significant hypertrophy of the remaining gland. Treatment with ACTH in the same age animal also causes a significant hypertrophy. The response in the 7-day old to unilateral adrenalectomy is significantly depressed as compared with that obtained in the 2-day old rat. Following treatment with ACTH, adrenal hypertrophy is greater in the 7-day old rat than in the 2-day old. It is concluded that the pituitary-adrenal axis is relatively refractory in the rat at about day 7 of age and is functional in both the younger and older animal.

Increased concentration of water in uterus of the rat following treatment with relaxin.

Conclusions Relaxin causes an increased concentration of water in the uterine tissue of the immature rat. Maximum hydration was obtained at 6 hours following administration of the hormone. The minimum effective dose of relaxin is 1 G.P.U. and the maximum response occurs following 10 G.P.U. relaxin. Contrary to the effect seen following estradiol administration, no secondary rise in uterine water content and no increase in dry weight is observed. Pretreatment with estrogen is not necessary for this action of relaxin on the water content of the uterine tissue.

Changes in Estrous Cycle of Rat During Prolonged Exposure to Cold.

Summary Studies on the reproductive activity of the adult female rat indicate a marked increase in length of the estrous cycle following exposure to a low ambient temperature. Duration of both the proestrous and estrous stages was increased whereas length of the metestrous and diestrous stages was decreased. Treatment with 50 μg of thyroxine prevented the abnormal changes in the estrous cycle during exposure to cold.

Atrophy of Adrenal Gland Following Thiouracil and Vit. B12.

Conclusions Vit. B12 prevented the growth inhibiting action of thiouracil but failed to prevent adrenal atrophy. Atrophy of the adrenal cortex was due to a specific action of the goitrogen and not a reflection of generalized inhibition of body growth.

Eosinophils of blood during prolonged exposure to cold and chronic administration of cortisone acetate.

Conclusions Evidence has been presented to show that the circulating eosinophils do not remain depressed in rats exposed to cold for a period of 90 days. The level of eosinophils dropped 6 hours after the animals were exposed to the cold, but returned to above the normal values within 48 hours and in general remained high for the duration of the exposure. Different doses of cortisone acetate were administered to intact rats and it was determined that a daily dose of 100 μg was necessary to maintain a depressed level of eosinophils during the period of treatment. The evidence suggests that a eucorticoid state may develop during adaptation to cold. The permissive action of the adrenal gland and its relation to the adaptation of rats to a low environmental temperature is discussed.