Effect of intrauterine devices on preovulatory LH and progesterone levels in the cyclic hamster.

Intrauterine devices do not affect the cycle length in mice (Bartke, 1970), hamsters (Orsini, 1965; Lau, Saksena & Chang, 1974) and rats (V. D. Castracane, S. K. Saksena & A. A. Shaikh, unpublished data) but cause a delay in post-coital ovulation in rabbits (Janakiraman & Casida, 1968). Ginther, Hawk & Casida (1966) reported an increase in the pituitary LH content of ewes carrying an IUD and IUDs have been reported to block ovulation in the Indian water buffalo (Buch, Shukla & Hawk, 1964). If a similar delay in ovulation or LH discharge could be demonstrated in IUD-bearing hamsters, these animals would provide a convenient model for the study of the mechanism of action of IUDs. Mature female golden hamsters (Mesocricetus auratus) weighing 130 to 140 g, obtained from a local breeder, were maintained at constant temperature (22 \m=+-\ 1\s=deg\C)and artificial lighting (07.00 to 19.00 hours). All females were examined daily for changes in vaginal discharge and were then grouped according to the stage of the oestrous cycle. At least two consecutive 4-day oestrous cycles were recorded for each animal before they were used for experiments. Under pentobarbital sodium anaesthesia, two pieces of 'Supramid extra' threads were inserted along the entire length of both uterine horns as described by Saksena & Harper (1974) between 09.00 and 09.30 hours on the day of pro-oestrus. The animals were then rested for two cycles. Peripheral blood samples were collected from the abdominal aorta in heparinized syringes on the day of pro-oestrus under pentobarbital sodium anaesthesia at the times indicated in Table 1. The blood was centrifuged and the plasma obtained was frozen until it was assayed for LH and progesterone. Peripheral plasma LH concentrations were determined by radioimmunoassay adapted from the method described by Niswender, Midgley, Monroe & Reichert (1968). The LH standard (LER-1213A) as determined by radioimmunoassay was 0-48 times as potent as NIH-LH-S12. Plasma LH concentra¬ tions were assayed in 400-μ1 aliquots. Ether extracts of the plasma without Chromatographie separation were assayed for progesterone by radioimmunoassay (Shaikh, 1972). The antiserum used in the assay exhibited a 90%, 35% and 1-2% cross-reaction with 17ahydroxyprogesterone, desoxycorticosterone and 20a-hydroxyprogesterone, res-