Robinson J J, Aitken R P, Atkinson T, Wallace J M, McNeilly A S
Rowett Research Institute, Aberdeen, UK.
J Reprod Fertil. 1996 May;107(1):17-22. doi: 10.1530/jrf.0.1070017.
Twelve anoestrous ewes maintained under natural photoperiod at 57 degrees N received an oral dose of 3 mg melatonin daily at 15:00 h from 1 May. Starting 41 days later and extending from 11 June until 5 September, six of the ewes were also infused continuously with 0.8 mg thyrotrophin-releasing hormone (TRH) day-1 via subcutaneous osmotic minipumps. The remaining six ewes acted as controls. Behavioural oestrus, ovulation rate and luteal function were determined by exposure to a vasectomized ram, laparoscopy and the measurement of progesterone in peripheral plasma, respectively. TRH infusion stimulated a sustained increase (P < 0.001) in plasma concentrations of thyroxine, tri-iodothyronine and prolactin (thyroxine: 158 +/- 9.3 and 65 +/- 7.7 nmol l-1 for TRH-infused and control ewes, respectively; tri-iodothyronine, 2.6 +/- 0.12 and 1.1 +/- 0.19 nmol l-1 and prolactin, 57 +/- 12 and 11 +/- 2 micrograms l-1). No ewes were in oestrus before TRH infusion and the mean number of behavioural oestrous cycles per ewe during the infusion period was 1.3 +/- 0.33 and 2.5 +/- 0.34 for TRH-infused and control ewes, respectively (P < 0.05). Corresponding mean intervals from 1 May to the onset of the first luteal phase (progesterone > 1 ng ml-1) were 88 +/- 8.9 and 79 +/- 3.5 days (not significant). TRH infusion had no effect on the mean numbers of corpora lutea (1.7 +/- 0.14 and 1.6 +/- 0.20 for TRH-infused and control ewes, respectively), but was associated with a lower mean incidence of normal luteal phases (1.5 +/- 0.43 versus 2.7 +/- 0.21, P = 0.052). Abnormalities in luteal function included delayed initial expression, extended ovarian cycles, suprabasal periovulatory progesterone concentrations and protracted periods of low progesterone secretion between successive ovarian cycles. Thus continuous TRH infusion suppressed plasma prolactin, doubled the circulating concentrations of thyroxine and tri-iodothyronine, and was associated with a wide range of abnormalities in ovarian function and endocrine status, the nature of which varied between ewes.
12只处于乏情期的母羊在北纬57度自然光照周期下饲养，从5月1日起每天15:00口服3毫克褪黑素。41天后开始，从6月11日持续到9月5日，其中6只母羊还通过皮下渗透微型泵每天持续输注0.8毫克促甲状腺激素释放激素（TRH）。其余6只母羊作为对照。分别通过与输精管结扎公羊接触、腹腔镜检查以及外周血浆中孕酮的测定来确定行为发情、排卵率和黄体功能。TRH输注刺激甲状腺素、三碘甲状腺原氨酸和催乳素的血浆浓度持续升高（P<0.001）（甲状腺素：TRH输注母羊和对照母羊分别为158±9.3和65±7.7纳摩尔/升；三碘甲状腺原氨酸，2.6±0.12和1.1±0.19纳摩尔/升，催乳素，57±12和11±2微克/升）。在TRH输注前没有母羊发情，在输注期间每只母羊行为发情周期的平均数，TRH输注母羊和对照母羊分别为1.3±0.33和2.5±0.34（P<0.05）。从5月1日到第一个黄体期开始（孕酮>1纳克/毫升）的相应平均间隔分别为88±8.9和79±3.5天（无显著差异）。TRH输注对黄体的平均数没有影响（TRH输注母羊和对照母羊分别为1.7±0.14和1.6±0.20），但与正常黄体期的平均发生率较低有关（1.5±0.43对2.7±0.21，P = 0.052）。黄体功能异常包括初始表达延迟、卵巢周期延长、排卵前孕酮浓度高于基础值以及连续卵巢周期之间孕酮分泌低的持续时间延长。因此，持续输注TRH会抑制血浆催乳素，使甲状腺素和三碘甲状腺原氨酸的循环浓度加倍，并与卵巢功能和内分泌状态的广泛异常有关，其性质在不同母羊之间有所不同。
