The Effects of Prolactin and Gonadotropin on Luteal Function and Morphology in the Cyclic Golden Hamster

Abstract

Abstract. The present study was conducted to evaluate the endocrinological effects of the pituitary on luteal maintenance and regression in the cyclic golden hamster (Mesocritus auratus). After hypophysectomy (Hypox) at 0900 h on day 1 of the estrous cycle (the day of ovulation), the animals received injection of prolactin (PRL) or PRL plus equine chorionic gonadotropin (eCG). They were decapitated at 1500 h on day 3 of the cycle, and trunk blood was collected for measurement of progesterone (P4). Corpora lutea (CLs) were dissected from one ovary for DNA ladder detection by electrophoresis, determination of DNA fragmentation ratio by fluorometric measurement method and measurement of P4. The other ovary was used for histological observation. After the Hypox, the daily injection of 1 mg ovine PRL restrained the DNA fragmentation ratio and number of apoptotic cell in the CLs. The PRL treatment maintained the luteal morphology and increased the luteal P4 concentration, but not in the plasma P4 concentration. In addition to PRL, injection of 2 IU eCG after the Hypox also restrained the DNA fragmentation ratio and number of apoptotic cells in the CLs to the level of a pregnant animal. The PRL plus eCG treatment maintained the luteal morphology in the same manner as the PRL only treatment and increased not only the luteal but also the plasma P4 concentration. These results suggest that PRL restrains luteal apoptosis and maintains luteal morphology and that the combination of PRL and eCG restrains not only structural but also functional luteal regression in the cyclic hamster. Key words: Apoptosis, Corpus luteum, Golden hamster (Mesocritus auratus), Hypophysectomy, Prolactin (PRL) (J. Reprod. Dev. 54: [418][419][420][421][422][423] 2008) he corpus luteum (CL) is a transient endocrine organ required for normal pregnancy in mammals. The most important function of the CL is to secrete progesterone (P4). If pregnancy does not occur, the CL must regress to allow initiation of a new reproductive cycle. Luteal function and structure are regulated by luteotropic and luteolytic hormones. Luteotropic hormones maintain and activate the CL, and luteolytic hormones lead the CL to regression. Whereas the factors regulating follicle development, ovulation and luteinization are common to many mammalian species, the luteotropic and luteolytic factors are different between species [1-3].The estrous cycle of the golden hamster lasts exactly 4 days (day 1=ovulation day), and the functional life span of the CL is limited to the first 2 days of the cycle. Serum P4 levels decrease drastically at the end of day 2 (functional luteal regression) [4]. Following functional regression, the CL shows signs of structural regression on day 3 of the cycle and vanishes by the next ovulation [5,6]. This rapidity of structural regression is a feature of hamster luteolysis. In the rat, although the functional life span of the CL is about 2 days as in the hamster, the luteal structure persists for 3-4 cycles [1,3]. This difference suggests that the regul...