Prolactin

About: Prolactin is a research topic. Over the lifetime, 22356 publications have been published within this topic receiving 609537 citations. The topic is also known as: lactotropin, & PRL,.

Alterations of Radioimmunoassayable Growth Hormone and Prolactin during Hypothyroidism

Abstract: Induction of hypothyroidism by treatment of rats with propylthiouracil (PTU) or radioactive iodine reduced pituitary and plasma growth hormone concentrations. Radioimmunoassayable pituitary and plasma growth hormone was diminished after three weeks of PTU ingestion. By four weeks, plasma growth hormone had fallen to barely detectable levels in most animals. Pituitary growth hormone concentration reached the lowest value by 40 days and remained depressed throughout 98 days of PTU ingestion. After treatment for 21 days with PTU, rats given tap water had progressively increasing pituitary growth hormone concentrations reaching control levels within 19 days. Rats given PTU and thyroxine injections to prevent hypothyroidism had no appreciable change in pituitary or plasma growth hormone concentrations. Administration of cortisol to chronically hypothyroid animals failed to increase pituitary growth hormone content. When rats bearing the growth hormone— and prolactin— producing tumor MtTWl5 were rendered hypoth...

Concentrations of reproductive hormones in canine serum throughout late anestrus, proestrus and estrus.

Abstract: Concentrations of estradiol, progesterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin in serum from 6 bitches bled daily for at least 45 days before the onset of proestrus, during proestrus and estrus were determined by radioimmunoassay. Mean concentrations of estradiol in serum were high early in the sampling period (20 to 46 pg/ml) and appeared to decrease prior to the onset of proestrus (8 to 19 pg/ml). There were sporadic increases in serum concentrations of LH throughout the sampling period in each bitch. Five of the 6 bitches sampled had increased serum concentrations of LH following the low mean concentration of estradiol just before the onset of proestrus. Mean concentrations of FSH were highest during anestrus (240 to 294 ng/ml) and near the time of the preovulatory surge of LH (297 ng/ml) and were lowest during proestrus (131 to 200 ng/ml). The mean concentration of progesterone for the 6 bitches remained at less than 1.0 ng/ml throughout late anestrus, but increased to greater than 1.0 ng/ml the day of the maximum mean concentration of LH (preovulatory LH surge). Mean concentrations of prolactin were variable throughout the sampling period and demonstrated no consistent pattern among bitches. The results of the current investigation suggest that neither the canine ovary nor pituitary are quiescent during anestrus. The bitch appears to have sufficient FSH present during anestrus for follicular growth. Serum concentrations of LH appear to increase prior to the onset of proestrus when concentrations of estradiol are lowest, possibly inducing a new follicular phase. Progesterone and prolactin do not appear to be involved in the termination of anestrus in the bitch.

Pregnancy-Induced Adaptation in the Neuroendocrine Control of Prolactin Secretion

Abstract: During pregnancy, neuroendocrine control of prolactin secretion is markedly altered to allow a state of hyperprolactinaemia to develop. Prolactin secretion is normally tightly regulated by a short-loop negative-feedback mechanism, whereby prolactin stimulates activity of tuberoinfundibular dopamine (TIDA) neurones to increase dopamine secretion into the pituitary portal blood. Dopamine inhibits prolactin secretion, thus reducing prolactin concentrations in the circulation back to the normal low level. Activation of this feedback secretion by placental lactogen during pregnancy maintains relatively low levels of prolactin secretion during early and mid-pregnancy. Despite the continued presence of placental lactogen, however, dopamine secretion from TIDA neurones is reduced during late pregnancy. Moreover, the neurones become completely unresponsive to endogenous or exogenous prolactin at this time, allowing a large nocturnal surge of prolactin to occur from the maternal pituitary gland during the night before parturition. In this review, we describe the changing patterns of prolactin secretion during pregnancy in the rat, and discuss the neuroendocrine mechanisms controlling these changes. The loss of response to prolactin is an important maternal adaptation to pregnancy, allowing the prolonged period of hyperprolactinaemia required for mammary gland development and function and for maternal behaviour immediately after parturition, and possibly also contributing to a range of other adaptive responses in the mother.