Effects of 2-Br- -ergocryptine on plasma prolactin level and milk yield in cows

Hormonal control of mammogenesis and onset of lactation in cows--a review

Estrogen stimulates development of mammary ducts, and progesterone and estrogen stimulate proliferation of secretory tissues. In vivo, sequential addition of insulin (step 1), glucocorticoid (step 2), and prolcatin (step 3) leads to biosynthesis of casein and lactose. In cows, mammogenesis continues until termination of pregnancy and overlaps onset of lactation. Progesterone probably inhibits differentiation of secretory cells at step 2 or step 3. Sensitivity of individual cells to progestational inhibition may decrease variably which may be interdependent upon relative increases in estrogen, prolactin, corticoids, and growth hormone to cause asynchronies among them at calving. Since prolactin in plasma is not correlated with progesterone or the estrogens, factors other than feed-back effects of ovarian steroids may be responsible for its sustained increase periparturiently. Also, elevated prolactin periparturiently may be unrelated to subsequent rates of lactation because its "basal" concentrations may meet requirements when inhibiting effects of progesterone are removed. This concept is attractive because mammary cells neither are synchronized highly for biosynthesis nor secrete normal milk for several days after calving. At the latter time, concentrations in plasma are low for progesterone and estrogen, similar to 3 days before calving for glucocoiticoids and prolactin, and increasing for insulin. Evidence of lactation under unusual circumstances was discussed.

Hormonal control of Luteal 20alpha-Hydroxy steroid dehydrogenase and delta5-3beta-hydroxy steroid dehydrogenase during luteolysis in the pregnant rat

Treatment of pregnant rats with human chorionic gonadotrophin, luteotrophin (luteinizing hormone), luteotrophin-releasing hormone, prostaglandin F2alpha, aminoglutethimide, or by foetoplacental removal or hysterectomy achieved a common multiple-response pattern, namely increased activity of luteal 20alpha-hydroxy steroid dehydrogenase with decreased activity of delta5-3beta-hydroxy steriod dehydrogenase and release of delta4-3-oxo steroids in vitro. 2. Similar effects of foetoplacental removal are noted in pregnant mice. 3. Gonadotrophin induced lower activities of 20alpha-hydroxy steroid dehydrogenase, except at the very end of pregnancy, and partly inhibited the induction caused by foetoplacental removal. 4. The results suggest that existence of a placental factor that restrains these changes until the end of normal pregnancy, which is produced in amounts proportional to the number of placentae and is conveyed to the ovary via the blood. 5. This factor was not replaced by prolactin. 6. It is argued that neither placental lactogen nor pituitary luteotrophin participate in the induction of 20alpha-hydroxy steroid dehydrogenase at late pregnancy in the rat. 7. Aminoglutethimide induced 20alpha-hydroxy steroid dehydrogenase only in late pregnancy. This was partly reversed by progesterone, wholly reversed by progesterone plus oestrogen, and did not involve the pituitary.

Milk secretory response of the conscious lactating rat following intravenous injections of rat prolactin

Mammary glands of rats on day 14 of lactation were emptied of milk by the pups after 8 h of nonsuckling with the aid of oxytocin injections to the mother. The glands subsequently refilled about 50% within 6 h and were completely refilled with mild within 16 h. Suckling for 5 min midway during the 8 h period of nonsuckling caused complete refilling of the glands within 6 h. Refilling within 6 h also occurred if, instead of suckling, rat prolactin was injected at 1 min intervals directly into the circulation of the conscious mother via an indwelling right atrial catheter. Five injections of 200 ng or three injections of 400 ng were without effect (in comparison with five injections of saline) upon mammary refilling whereas 10 injections of 200 ng or four injections of 400 ng simulated significant but submaximal refilling. Complete refilling resulted from five injections of 400 ng. Prolactin is secreted steadily over prolonged periods of suckling in the rat, but only that prolactin released during the first few minutes of suckling appears to be required for milk secretion.

Interspecies study on the effect of perphenazine on milk yield and composition

The effects on lactation of perphenazine, a tranquillizer which increases the level of prolactin in the blood, have been studied in cows, goats, guinea-pigs and rabbits. The drug caused a significant depression of milk yield in cows, goats and rabbits, but was without effect on the milk yield of guinea-pigs. It seems probable that the inhibitory effects on lactation were due to the actions of the drug on appetite and behaviour. It is concluded that perphenazine, because of its other actions, is not a suitable agent for studying the physiological effects of increased levels of endogenous prolactin.

Inhibition of cyclic gonadotropin secretion by endogenous human prolactin

The resumption of cyclic uterine bleeding reportedly accompanies the use of human prolactin (HPRL)-suppressing agents in postpill galactorrhea-amenorrhea. In this laboratory, HPRL suppression with L-dopa was variable and short lived. Basal plasma HPRL levels were elevated before and after as much as five months of therapy. Galactorrhea persisted and mean gonadotropin concentrations were subnormal. An immediate and sustained attenuation of HPRL secretion ( less than 200 per cent) followed the use of 2-Br-alpha-ergocryptine (CB-154). Cyclic gonadotropin secretion resumed and was accompanied by ovulation and, in one instance, pregnancy. The cessation of galactorrhea was positively correlated with the rise in the daily concentration of 17 beta-estradiol. Cyclic postovulatory menstruation continued after the cessation of CB-154 treatment. HPRL levels remained normal. The daily patterns of human follicle-stimulating hormone (HFSH) and human tuteinizing hormone (HLH) secretion created by the suppression of HPRL displayed an inherent rhythmicity identical to that observed at the time of menarche. The inhibitory effects of HPRL appeared directed at cyclic rather than tonic gonadotropin secretion. At the same time, diminished ovarian estrogen production seemed to increase mammary gland sensitivity to HPRL, leading to lactation. One may postulate, therefore, that the ingestion of sex steroids is associated with an over-all suppression of endogenous cyclic and, to a lesser extent, tonic gonadotropin secretion secondary to which ovarian function is attenuated. Without physiologic concentration of circulating estrogen, HPRL induces mammary alveolar function with the production of a milklike secretion.