Multiple progesterone injections and the duration of estrus in ovariectomized guinea pigs

Abstract

The duration of sexual receptivity in guinea pigs primed with 3.3 ug estradiol benzoate and given 0.1 mg progesterone 36 hr later in oil or propylene glycol vehicle was about 6–7 hr. Maintenance of elevated plasma progesterone levels (as measured by radioimmunoassay)throughout the period of heat by multiple 0.1 mg progesterone injections significantly prolonged (by about 2.7 hr) heat duration, but heat terminated despite the presence of high plasma progesterone levels. The experiment suggests that a decline in plasma progesterone concentration is not necessary for the termination of heat. Methods by which termination of heat could occur are discussed.