Effects of varying doses of HCG on the evolution of preovulatory rabbit follicles and oocytes

Abstract

To determine the effects of insufficient or excessive doses of human chorionic gonadotrophin (HCG) on ovulation, varying single doses from 5 to 100 IU were administered to 40 does in oestrus. A total of 371 preovulatory follicles and oocytes were observed. Low doses of HCG (5-10) started resumption of meiosis, but no ovulation occurred. Higher doses progressively induced nuclear maturation (prometaphase, metaphase I, metaphase II). Simultaneously increasing doses initiated ovulation of some of the follicles, then of most of the follicles. Unruptured follicles, mostly with oocytes in metaphase II were frequent and depending on the dose, these were preovulatory, haemorrhagic or luteinized. The administration of different doses demonstrated the possible dissociation of several mechanisms leading to ovulation. The induction of nuclear maturation requires lower doses of HCG than luteinization. Follicular rupture requires even higher doses. Premature luteinization induces intrafollicular ovum retention without (LUF syndrome) or with follicular rupture. These mechanisms of ovulation explain the effects of blunted luteinizing hormone surges or inadequate HCG administration.

Cetrorelix suppresses the preovulatory LH surge and ovulation induced by ovulation-inducing factor (OIF) present in llama seminal plasma

“…Although the CL diameter profile did not differ between OIF- and GnRH-treated llamas, plasma progesterone was elevated in the former. The relationship between the degree of luteogenesis and the duration of the preovulatory LH surge elicited by OIF warrants further investigation, but is consistent with studies in primates and laboratory species [53-56]. …”

Administration of low-dose LH induces ovulation and prevents vascular hyperpermeability and vascular endothelial growth factor expression in superovulated rats

“…This has already been described in rabbits by Bomsel-Helmreich et al (1989), who have shown that lower doses of hCG induce nuclear maturation; luteinization required higher doses and it was only the highest dose of hCG that induced follicular rupture. This may also be the case in humans where a time-or dose-dependent phenomenon leads to the initial rise in progesterone 12 h before the LH surge, the complete maturation of the oocyte 32 h after the surge and follicular rupture 36 h after the LH surge (Hoff et al 1983, Speroff et al 1999, Yeh & Adashi 1999.…”

Morphological Features and Effects on Reproductive Parameters of Ovarian Cysts of Follicular Origin in Superovulated Rabbit Does

“…Luteal cysts had a follicular wall increased in thickness as compared with follicular cysts, hypertrophy and luteinization of follicular cells, breakdown of the basement membrane and the follicular antrum filled with RBC. This last fact gives the characteristic red colour to the luteal cysts of rabbit does, usually referred to in the literature as haemorrhagic or blood follicles (Allen et al 1947;Adams 1982;Bomsel-Helmreich et al 1989. In the present study, a third type of ovarian cysts, referred as mixed cysts, has also been described.…”