In vitro release of luteinizing hormone releasing hormone (LH-RH) from the hypothalamus in pregnant rats.

Using the superfusion system, the basal LH-RH release from the hypothalamus was investigated during pregnancy in rats. Pregnant rats were sacrificed on day 10, 15, 18 and 21 of pregnancy by decapitation. The hypothalamus was taken out as a block, and superfused with Krebs-Ringer bicarbonate buffer in conditions of 37 degrees C, 95% O2 + 5% CO2. The changes in LH-RH concentrations in the superfused medium were measured using a radioimmunoassay for LH-RH. Serum LH levels were significantly decreased from day 10 to 15, but increased rapidly from day 18 to 21. On the other hand, the release of LH-RH from the hypothalamus remained stable until day 18, followed by a significant increase on day 21. These results suggested that the decrease in LH secretion from day 10 to 15 would not be due to the changes in LH-RH release, while the increase in serum LH levels on day 21 might depend on the increase in the release of LH-RH.