Ovariectomy and suckling intensity effects on mammary nucleic acid, prolactin, and ACTH

Abstract

The role of the ovary in mammary growth and metabolism with increased suckling was studied in lactating rats. At parturition rats were left intact, sham ovariectomized, or ovariectomized. Ovariectomized rats at days 8 anp 16 contained an average of 10.3 and 3.5%, respectively, (P < 0.01) less mammary DNA and 11.0 and 3.6%, respectively, (P < 0.05) less mammary RNA than control rats. However, glands of ovariectomized rats increased more than 56% in DNA and 137% in RNA as suckling increased from two to six pups. Although litter weight gains between days 7 and 16 of lactation were not affected (P > 0.05), total litter weights at days 7, 8 and 16 were reduced (P < 0.01) by ovariectomy. Increasing the suckling from two to six pups increased prolactin from .027 to .049 IU/mg pituitary. Ovariectomy reduced prolactin content 42%, whereas ACTH was unaffected when compared with sham-ovariectomy. Pituitary glands of rats suckling two pups contained 104 and 24% more ACTH than those of rats suckling four or six pups, respectively. The results suggest that the ovary and ACTH may be of secondary importance to prolactin in promoting maximal mammary development and synthetic activity with increased nursing.