Heat stress disrupts reproductive function in cattle. In summer, high ambient temperature and humidity elevate core body temperature, which is considered to be detrimental to reproductive abilities in cattle. Neurokinin B (NKB) is a factor that generates pulsatile GnRH and subsequent LH secretion in mammals. Recent studies have reported that NKB-neurokinin 3 receptor (NK3R) signaling is associated with heat-defense responses in rodents. The present study aimed to clarify the role of NKB-NK3R signaling in thermoregulation in cattle. We examined the effects of an NK3R-selective agonist, senktide, on vaginal temperature as an indicator of core body temperature in winter and summer. In both seasons, continuous infusion of senktide for 4 h immediately decreased vaginal temperature, and the mean temperature change in the senktide-treated group was significantly lower than that of both vehicle- and GnRH-treated groups. Administration of GnRH induced LH elevation, but there was no significant difference in vaginal temperature change between GnRH- and vehicle-treated groups. Moreover, we investigated the effects of senktide on ovarian temperature. Senktide treatment seemed to suppress the increase in ovarian temperature from 2 h after the beginning of administration, although the difference between groups was not statistically significant. Taken together, these results suggest that senktide infusion caused a decline in the vaginal temperature of cattle, in both winter and summer seasons, and this effect was not due to the gonadotropin-releasing action of senktide. These findings provide new therapeutic options for senktide to support both heat-defense responses and GnRH/LH pulse generation.

热应激会破坏牛的生殖功能。夏季，高环境温度和湿度会升高核心体温，这被认为不利于牛的繁殖能力。神经激肽 B (NKB) 是一种在哺乳动物中产生脉动 GnRH 和随后 LH 分泌的因子。最近的研究报告称，NKB-神经激肽 3 受体 (NK3R) 信号传导与啮齿动物的热防御反应有关。本研究旨在阐明 NKB-NK3R 信号在牛体温调节中的作用。我们研究了 NK3R 选择性激动剂 senktide 对作为冬季和夏季核心体温指标的阴道温度的影响。在两个季节，连续输注森克肽 4 小时都会立即降低阴道温度，senktide 治疗组的平均温度变化显着低于载体和 GnRH 治疗组。GnRH 的给药诱导 LH 升高，但 GnRH 治疗组和载体治疗组之间的阴道温度变化没有显着差异。此外，我们研究了senktide对卵巢温度的影响。Senktide 治疗似乎从给药开始后 2 小时起抑制了卵巢温度的升高，尽管组间差异无统计学意义。综上所述，这些结果表明，在冬季和夏季，森克肽输注导致牛的阴道温度下降，这种影响不是由于森克肽的促性腺激素释放作用。