Date of Award
Dissertation - Restricted
Doctor of Philosophy (PhD)
Bela E. Piacsek
Victor de Vlaming
Robert H. Fitts
Prolactin is secreted by the anterior pituitary and is under the control of a secretion from the hypothalamus called prolactin inhibitory factor (PIF) which is directed to the pituitary by way of the median eminence. Prolactin secretion by the in site pituitary is inversely proportional to the secretion of PIF. The influence of the PIF is lost or greatly reduced when the pituitary is transplanted to an exogenous site which results in a marked increase in prolactin secretion.
In the female rat there is a prolactin surge on the afternoon of proestrous. In the pseudopregnant and pregnant rat, prolactin is secreted according to a diurnal rhythm and is responsible for maintenance of the corpus luteum and progesterone secretion. Prolactin in combination with progesterone promotes growth of the alveolar lobules in the mammary glands and after parturation, prolactin along with insulin and adrenal corticoids initiates and maintains milk secretion.
In the male rat, prolactin in combination with LH stimulates testosterone secretion and in combination with testosterone stimulates growth of secondary sex tissues, however in the male rat these effects appear to be somewhat less than critical. Many aspects of prolactin in the male have not been investigated including the 24-hour secretory pattern, the effects of excessive or deficient serum prolactin concentrations in adults and the importance of prolactin to the normal development of immature male rats.
The first manuscript in this thesis investigated the secretory pattern of prolactin throughout a 24-hour period. In addition, the secretory pattern of other tropic hormones and testosterone were investigated primarily to determine if any obvious relationships exist between the secretion of prolactin and these other hormones.
The second study investigated prolactin function by monitoring the effects of chronic prolactin deficiency on the development of secondary sex structures and on the secretion of other hormones. Prolactin deficiency was initiated and maintained by periodic injections of an antiserum to rat prolactin. The third study was an investigation to determine if the sequence of events leading to the diurnal prolactin rhythm, which was discovered in the first study, was dependent on the presence of the adrenal glands.