Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)




One major function of prolactin in the female is the stimulation of mammary gland development for lactation. It is well established in the rat that during periods of lactation, when serum prolactin levels are high, there is a suppression of the serum luteinizing hormone level. Prolactin has also been shown to inhibit the postcastration rise in serum luteinizing hormone in rats. Work addressing the question of site and mechanism of action of the inhibition of gonadotropin secretion by prolactin has focused on the relationship between the hypothalamus and the pituitary, and the relationship between the different cell types in the anterior pituitary.

The present study was undertaken to assess the changes that take place in the relationships between lactotropes and luteotropes in the anterior pituitary of the rat in response to varying levels of lactational stimuli. Using specific immunogold staining and TEM, cellular associations between luteotropes and lactotropes were quantitated. The average number of cell associations for five study groups was determined to be 2.43 $\pm$ 0.03 for the control groups, 2.55 $\pm$ 0.11 for sham ovariectomized animals, 1.63 $\pm$ 0.13 for animals receiving ovariectomy and nursing ten pups, 1.63 $\pm$ 0.18 for animals that were intact and nursing ten pups and 1.82 $\pm$ 0.11 for animals that were intact and nursing two pups. These values were correlated with the hormonal status of the animals in each study group and to the level of lactational stimulus determined by the number of suckling pups.

The results show a high degree of negative linearity (r = 0.99) between serum prolactin and the number of cell associations observed in each group. There was also a strong positive linear relationship between serum luteinizing hormone and the mean number of cell associations for each group (+0.56). These data indicate that a paracrine moldulation of lactotrope and luteotrope activity may exist in the anterior pituitary of the female rat.

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