Automatic Control of LH and FSH Secretion by Short Feedback Circuits in Immature Rats

Immature rats 31–32 days old received intracerebral implants of LH, FSH and cholesterol. Twenty-seven gauge needles loaded at the tip with LH or FSH were stereotaxically implanted in the medial basal hypothalamus (MBH) and into the adenohypophysis; other animals were also implanted with FSH in the septum, rostral hypothalamus and subcutaneously. LH median eminence implants induced, 10–18 days later, a marked atrophy of the ovaries (p<0.005), and the percentage of rats which presented corpora lutea (CL) was significantly less than controls (16.6 vs. 75.6%; p<0.005). Rats with LH implanted in other areas did not modify their ovarian weight, and the percentage of CL was similar to controls. Animals with intrapituitary LH behaved as controls. Rats withimplants of FSH in the MBH and killed 7–12 days later did not present atrophy of the ovaries, and the histology showed a clear stimulation of the interstitial tissue with luteinization and multiple presence of CL. The percentage of rats with CL killed 4–12 days post implantation was significantly greater than the percentage of all the control groups. Rats with intrapituitary FSH or in other brain areas behaved as controls. It is suggested that in the immature rat the secretions of LH and FSH are automatically controlled by a negative and a positive short feedback mechanism, respectively, and that the 2 mechanisms are apparently located at different hypothalamic sites. (Endocrinology84: 786, 1969)