Changes in Concentration of Prolactin and Adrenal Corticosteroids in Rat Plasma During Pregnancy and Lactation

Abstract

In spite of the importance of prolactin and adrenal corticosteroids in the normal control of the mammary gland (Cowie & Tindal, 1971) there has been no report of their simultaneous measurement in rat plasma during pregnancy and lactation. There is no agreement on the pattern of change in corticosteroid concentration at the time of lactogenesis and parturition (Gala & Westphal, 1965;Kuhn, 1969).Primiparous CFE strain rats, allotted randomly to groups on day 0 of pregnancy, were decapitated without prior disturbance within 1 min after removal from their cage, between 08.30 and 09.30 h. Plasma was stored at \m=-\20\s=deg\C,total body weight after bleeding and adrenal weight were recorded. The day on which a vaginal plug was found and the day of parturition were designated day 0 of pregnancy and lactation respectively. Litter size was adjusted to six on day 0 of lactation.Plasma prolactin concentration was assayed in triplicate for each rat by the National Institute of Arthritis and Metabolic Diseases (NIAMD) rat-prolactin radioimmunoassay (Neill & Reichert, 1971) against the standard rat prolactin preparation (NIAMD RP-1 30i.u./mg). Corticosteroid concentration was measured in 0-01 ml duplicate samples of plasma per rat by the competitive protein-binding radioassay of Murphy (1967). [l,2-3H]Corticosterone (sp. act. 49-5 Ci/mmol, New England Nuclear Corporation), and corticosterone (4-pregnen-ll/?,21-diol-3,20-dione, Mann Research Laboratories) were used as the tracer and standard respectively. Plasma prolactin concentration decreased from 114-4 + 19-4 (s.e.m.) ng/ml on day 0 of pregnancy to a low of 21-0 + 1-4 ng/ml on day 10 of pregnancy, then increased to approximately 33 ng/ml on days 15 and 18 of pregnancy, and reached a peak of 133-0 + 34-5 ng/ml on day 5 of lactation. The concentration of prolactin gradually declined to 46-1 + 9-9 ng/ml on day 20 of lactation (Fig. 1). This is in agreement with the work of Amenomori, Chen & Meites (1970). Increased within-group variation during lactation was probably due to the effect of suckling, since studies in our laboratory as well as in others have shown that suckling stimulates the release of prolactin.Plasma corticosteroid concentration showed a high degree of within-group varia¬ tion with no significant differences between groups throughout pregnancy and % Present address:

Relationship of Prolactin and Growth Hormone to Mammary Function During Pregnancy and Lactation in the C3h/St Mouse

“…The levels of serum and pituitary prolactin found in these mice were strikingly similar to those reported in the rat (Reece & Turner, 1937;Grosvenor & Turner, 1960;Amenomori, Chen & Meites, 1970;Simpson, Simpson, Sinha & Schmidt, 1973). In general, prolactin levels in serum were low through most of pregnancy, and it was only near term that the concentrations rose to any marked extent.…”

“…Although blood was sampled in our study between 09.00 and 10.00 h, a small peak of serum prolactin on day 5 was nonetheless evident. Such a brief rise in serum prolactin in early gestation was also noted by Amenomori et al (1970), Linkie & Niswender (1972) and Simpson et al (1973). Although we did not detect a simultaneous increase in total mammary DNA or RNA content in our experiments, Traurig (1967) observed a high rate of cell proliferation in the mammary gland at this time.…”

Thermal limitation of mother–young contact in norway rats

“…Removal of the ovaries alone or the adrenal medulla alone did not affect either maternal core temperature or contact time, while removal of the entire adrenal gland (with both medulla and cortex) decreased maternal temperature and increased maternal contact time to the same extent as the double operation . These data suggested that adrenocortical glucocorticoids, which are normally elevated during lactation (Simpson, Simpson, Sinha, & Schmidt, 1973), induce the chronic increase in maternal temperature. This notion was reinforced when demonstrated that replacement therapy with corticosterone and cortisol, but not aldosterone (the dominant adrenal mineralcorticoid) or progesterone (the precursor of both adrenal mineral-and glucocorticoids), restored the normally elevated maternal temperature and normal contact pattern.…”

Fluid reabsorption by the proximal convoluted tubule of the kidney in lactating rats.

“…Direct perfusion of distal convoluted tubules indicated the occurrence of a similar phenomenon (Morgan & Berliner, 1969;Wright, 1982). However, the increased plasma concentrations of progesterone (Pepe & Rothchild, 1974;Arthur & Green, 1983) prolactin (Simpson, Simpson, Sinha & Schmidt, 1973;273 S. K. ARTHUR AND R. GREEN Arthur & Green, 1983) and corticosterone (Simpson et al 1973) during lactation might be responsible for the increased distal reabsorption. Neither progesterone nor prolactin concentrations mirror the changes in renal function (Arthur & Green, 1983) but the role of corticosterone is not clear.…”