Changes in the isoelectric focusing profile of pituitary follicle-stimulating hormone in the developing male rat.

Pituitary glands, hypothalami, and trunk blood were obtained from male rats at 5, 15, 18, 21, and 29 days of age, on the day of balanopreputial separation (Days 42-45), and during adulthood. The forms of follicle-stimulating hormone (FSH) present within each pituitary were separated by polyacrylamide gel isoelectric focusing. Serum and pituitary gonadotropins, hypothalamic luteinizing hormone-releasing hormone (LHRH), and the profile of FSH forms across the isoelectric focusing gel were determined by radioimmunoassay. No change in the relative proportions of FSH forms were observed between 5 and 21 days of age. Likewise, only slight changes in serum and pituitary gonadotropin levels and hypothalamic LHRH content were observed at these times. After 21 days of age, dramatic increases in serum and pituitary gonadotropin levels were observed. Similarly, a shift in FSH forms within the pituitary to more basic and bioactive forms was observed at this time. These results demonstrate that, during the transition through puberty in the male rat, not only the absolute amount, but also the isoelectric focusing profile, of FSH change.