Intravenous administration of progesterone and the onset of receptivity in female hamsters.

Progesterone-facilitated receptivity is believed to be a genomically mediated event. However, in contrast to estrogen, progesterone's effects occur rapidly. This experiment was designed to examine the temporal onset of receptivity in hamsters following intravenous (IV) administration of progesterone. Ovariectomized female hamsters were tested for their responsiveness to 10 micrograms estradiol benzoate (EB) plus 0, 50, or 200 micrograms progesterone, administered subcutaneously (SC). The hamsters were tested for sexual receptivity at 0.5, 1, 1.5, 2, 3 and 4 h. Three days later they were fitted with jugular catheters. Two days after catheter implantation they received 10 micrograms EB SC; 48 h later they were tested for receptivity and then received an IV injection of 0, 50, or 200 micrograms progesterone in 0.2 ml propylene glycol. Following the IV P injection the animals were again tested at 0.5, 1, 1.5, 2, 3 and 4 h. Progesterone administration (either SC or IV) resulted in an increase in total lordosis duration (TLD) over time. TLD had significantly increased from the pre-progesterone levels by 2 h after 50 micrograms progesterone IV. In contrast, 50 micrograms progesterone SC did not cause an increase in TLD until 3 h postinjection. Moreover, in comparison to SC administration, the effects of IV progesterone were short-lived; TLD was significantly decreased by 4 h after injection. Following 200 micrograms progesterone, the latency to respond was shorter than with 50 micrograms progesterone (1.5 vs. 2 h). There was no difference in the onset of receptivity as a function of route of administration at the 200 micrograms dose.(ABSTRACT TRUNCATED AT 250 WORDS)