| Abstract: | ![]()
Luteal cell structure and function were studied by electron microscopy in conjunction with measurement of progesterone production by corpora lutea which were isolated and incubated in vitro on successive days of the four-day hamster estrous cycle. Granulosal cells were primarily responsible for the formation of the corpus luteum. Agranular endoplasmic reticulum and lipid droplets developed during luteinization of granulosal cells on the first post-ovulation day (day 1). Luteal cell hypertrophy on day 2 resulted from dilation of tubular agranular endoplasmic reticulum and swelling of mitochondria with tubular cristae. Plasma progesterone levels on the first two days of the cycle appeared to be correlated with luteal activity as corpora lutea were demonstrated to synthesize progesterone during this interval. Luteolysis occurred on day 3 with a reduction in luteal cell size accompanied by condensation of the agranular endoplasmic reticulum, regressive changes in the mitochondria, and a marked drop in luteal progesterone synthetic activity. On day 4, extensive phagocytic activity and luteal cell autolysis indicated an advanced involutional state. The short but functional luteal phase in the cyclic hamster does not appear to involve the production of 20α-hydroxy-pregn-4-en-3-one as occurs in the rat. This progestin was not detectable in plasma or luteal tissue before or after incubation at any time during the cycle. Possible mechanisms regulating luteal cell development and regression during the estrous cycle are discussed. |
