Relationship of oestrus synchronization method, circulating hormones, luteinizing hormone and prostaglandin F-2α receptors and luteal progesterone concentration to premature luteal regression in superovulated sheep

• Published in: Journal of reproduction & fertility Vol. 93; no. 1; p. 19
• Main Authors: Schiewe, M C, Fitz, T A, Brown, J L, Stuart, L D, Wildt, D E
• Format: Journal Article
• Language: English
• Published: England Society for Reproduction and Fertility 01.09.1991
• Subjects: Animals; Corpus Luteum - chemistry; Corpus Luteum - drug effects; Dinoprost - pharmacology; Estradiol - blood; Estrus Synchronization; Female; Follicle Stimulating Hormone - blood; Luteinizing Hormone - blood; Luteolysis; Progesterone - analysis; Progesterone - blood; Receptors, LH - analysis; Receptors, Prostaglandin - analysis; Sheep - physiology; Superovulation - physiology
• ISSN: 1470-1626; 0022-4251; 1741-7899
• DOI: 10.1530/jrf.0.0930019

Ewes were treated with exogenous follicle-stimulating hormone (FSH) and oestrus was synchronized using either a dual prostaglandin F-2α (PGF-2α) injection regimen or pessaries impregnated with medroxy progesterone acetate (MAP). Natural cycling ewes served as controls. After oestrus or AI (Day 0), corpora lutea (CL) were enucleated surgically from the left and right ovaries on Days 3 and 6, respectively. The incidence of premature luteolysis was related ( P < 0·05) to PGF-2α treatment and occurred in 7 of 8 ewes compared with 0 of 4 controls and 1 of 8 MAP-exposed females. Sheep with regressing CL had lower circulating and intraluteal progesterone concentrations and fewer total and small dissociated luteal cells on Day 3 than gonadotrophin-treated counterparts with normal CL. Progesterone concentration in the serum and luteal tissue was higher ( P < 0·05) in gonadotrophin-treated ewes with normal CL than in the controls; but luteinizing hormone (LH) receptors/cell were not different on Days 3 and 6. There were no apparent differences in the temporal patterns of circulating oestradiol-17β, FSH and LH. High progesterone in gonadotrophin-treated ewes with normal CL coincided with an increase in total luteal mass and numbers of cells, which were primarily reflected in more small luteal cells than in control ewes. Gonadotrophin-treated ewes with regressing CL on Day 3 tended ( P < 0·10) to have fewer small luteal cells and fewer ( P < 0·05) low-affinity PGF-2α binding sites than sheep with normal CL. By Day 6, luteal integrity and cell viability was absent in ewes with prematurely regressed CL. These data demonstrate that (i) the incidence of premature luteal regression is highly correlated with the use of PGF-2α; (ii) this abnormal luteal tissue is functionally competent for 2–3 days after ovulation, but deteriorates rapidly thereafter and (iii) luteal-dysfunctioning ewes experience a reduction in numbers of small luteal cells without a significant change in luteal mass by Day 3 and, overall, have fewer low-affinity PGF-2α binding sites. Keywords: sheep; superovulation; premature luteal regression; prostaglandin F-2α; receptor