Summary. In non-pregnant goats, appreciable amounts of testosterone (2·1 ng/g) and 5α-dihydrotestosterone (DHT, 0·8 ng/g) were present in the corpus luteum on Day 12 of the oestrous cycle. Significant (P < 0·01, N = 18) veno-arterial concentration differences of testosterone were found across ovaries bearing corpora lutea. No such difference in testosterone concentration occurred across ovaries without corpora lutea (P > 0·5, N = 12). Increased peripheral plasma concentrations of testosterone and DHT occurred at the start of luteal regression, as monitored by progesterone concentration, and before the day of oestrus. Subcutaneous injections of spironolactone (10mg/kg/day) in peanut oil between Days 10 and 20 of the oestrous cycle inhibited the increase in testosterone and DHT concentrations and delayed luteolysis and oestrus. It is suggested that aromatization of testosterone to oestrogens is needed for luteal regression and expression of oestrus in goats.
A. M. Homeida and M. M. Al-Eknah
Summary. Early corpus luteum development in nonpregnant and pregnant goats was characterized by a steady increase in peripheral plasma concentrations of progesterone and a high release of prostacyclin (PGI-2) but low release of prostaglandin F-2α (PGF2α). Jugular administration of oxytocin antagonist (OXA) (0·2 μg/kg/day) on the day of oestrus and for 3 days thereafter to cyclic and mated goats, significantly (P < 0·001) inhibited progesterone and prostaglandin secretion and reduced conception rate. Co-administration of PGI-2 (200 μg/day) with OXA resulted in a steady increase of progesterone and establishment of pregnancy, but co-administration of PGF-2α (175 μg/day) with OXA had no effect. It is suggested that oxytocin is required for early development of the corpus luteum and such effects may be mediated via PGI-2 production.
Keywords: oxytocin; oestrous cycle; prostaglandins; goat
A. M. Homeida and A. I. Al-Afaleq
Oxytocin at a dose of 100 iu injected s.c. daily into goats (Capra hircus) between day 3 and day 6 of the oestrous cycle caused a significant increase in testosterone secretion and luteolysis compared with saline-treated animals. Intrauterine administration of recombinant ovine interferon tau (80, 160 or 320 μg day−1) between days 12 and 18 of the oestrous cycle, or concomitantly (80 μg day−1) with oxytocin between day 3 and day 7, delayed luteolysis and blocked the increased release of testosterone. It is suggested that recombinant ovine interferon tau can act as an antiluteolytic agent in goats.
R. G. Cooke and A. M. Homeida
Summary. Jugular administration of 200 μg PGI-2 salt significantly reduced spontaneous uterine activity in ovariectomized, oestrogen-primed goats; the effect was acute and persisted for about 3 h. Peripheral plasma concentrations of 6-keto-PGF-1α, the stable metabolite of PGI-2, decreased to 50% of initial values after 30 min; but at the start of uterine recovery were in excess of 2 ng.ml−1. Uterine reactivity to both oxytocin and PGF-2α after PGI-2 administration was unaffected.
Keywords: prostacyclin; uterus; motility; goat; PGF-2α; oxytoxin
A. M. Homeida and Amna E. Khalafalla
Summary. Oxytocin at a dose of 100 i.u. injected subcutaneously (s.c.) daily to goats between Days 3 and 6 of the oestrous cycle caused a significant increase in testosterone secretion compared with saline-treated animals. An oxytocin antagonist (0·2 μg/kg) injected intra-arterially between Days 12 and 18 of the oestrous cycle or simultaneously with oxytocin between Days 3 and 6 blocked the increased release of testosterone and occurrence of oestrus. It is suggested that oxytocin-induced oestrus may occur via testosterone secretion.
Keywords: oxytocin; testosterone; oestrous cycle; goat
R. G. Cooke and A. M. Homeida
Summary. Active immunization against oxytocin significantly prolonged the oestrous cycle in 3 out of 4 goats; the mean (± s.e.m.) cycle length was 29·1 ± 1·7 days (n = 12) compared to 19·4 ± 0·6 days (n = 9) in control animals. During Days 10–21 of the cycle in the 3 responsive goats, peripheral plasma concentrations of progesterone and oxytocin were steady and those of 13,14-dihydro-15-keto-prostaglandin F-2α were very low (50–100 pg·ml− 1) with no marked pulsatile activity. The major effect of immunization would appear to be suppression of the synthesis of the uterine luteolysin PGF-2α, thus confirming that endogenous oxytocin has a facilitatory role in luteolysis via prostaglandin production.
A. M. Homeida, M. G. R. Khalil, and A. A. M. Taha
Summary. Peripheral plasma concentrations of progesterone, total oestrogens and testosterone (measured by RIAs) and LH (monitored by the mouse Leydig cell bioassay) were measured in 8 female camels for a complete oestrous cycle (23·1 ± 1·2 days). The absence of an LH surge and a low concentration of progesterone (< 1 ng/ml) during oestrus (5 days) and throughout the cycle indicated a failure of spontaneous ovulation and absence of a subsequent luteal phase in this species. High concentrations of testosterone and oestrogens indicated that the oestrous cycle in the camel is mostly follicular and that the increasing values of the two hormones during follicular development (5 days) is probably the stimulus to behavioural oestrus.
Keywords: camel; oestrous cycle; LH; progesterone; oestrogens; testosterone