Hormonal regulation of the number and activity of ribosomes in mammary gland explants of mice.

Possible effects of insulin, hydrocortisone and prolactin on the number and activity of ribosomes enganged in protein biosynthesis in mammary gland explants were explored. The rate and extent of [3H]-puromycin attachment to nascent peptides was used to assess, respectively, the activity and number of ribosomes engaged in protein biosynthesis. None of the hormones altered the number of ribosomes engaged in protein biosynthesis. In addition, of the hormones tested, only insulin appeared to accelerate the rate at which ribosomes carried out the translocation process. The early (1 hr) effect of insulin on protein biosynthesis in the mammary gland would therefore appear to occur via an activation of ribosomal activity. In contrast, the early (6 hr.) effect of prolactin on protein biosynthesis would appear to be exclusively via an RNA-DNA dependent mechanism.