Effects of Estrogen on Growth Hormone Pulsatility in Peripheral Blood and Neuropeptide Profiles in the Cerebrospinal Fluid of Goats

Abstract

Abstract. We previously reported that growth hormone (GH) pulses were negatively associated with neuropeptide Y (NPY) profiles in cerebrospinal fluid (CSF) of the third ventricle of Shiba goats. In addition, while most GH pulses were coincident with GH-releasing hormone (GHRH) pulses, there was no correlation between GH and somatostatin (SRIF) levels. The present study was performed to elucidate the relationship between GH pulses and these neuropeptide levels in CSF when estradiol (1.0 mg/head) was subcutaneously administered to ovariectomized goats. CSF and plasma samples were collected every 15 min for 18 h (from 6 h before to 12 h after injection). GH levels in peripheral blood and GHRH, SRIF and NPY levels in CSF were measured by radioimmunoassay. Pulse/trough characteristics and correlations were assessed by the ULTRA algorithm and cross-correlation analysis. Before estradiol was injected, significant coincidence was found between GHRH pulses and GH pulses, and negative coincidence was found between NPY troughs and GH pulses. Six to 12 h after estradiol injection, the amplitude and area under the curve (AUC) of the GH pulses were markedly increased. The duration and AUC of the GHRH pulses in the CSF were also increased, and stronger synchrony of GHRH with GH was observed. In contrast, the baseline of NPY was significantly decreased, and the negative correlation between the GH pulses and NPY troughs disappeared. The parameters of SRIF troughs were not clearly changed. These observations suggest that estrogen enhances the pattern of secretion of GH in the goat via enhancement of GHRH pulses and decrease of NPY levels. Key words: Estrogen, Growth hormone, Growth hormone-releasing hormone, Neuropeptide Y, Somatostatin (J. Reprod. Dev. 57: [280][281][282][283][284][285][286][287] 2011) rowth hormone (GH) is secreted in a pulsatile fashion in various mammalian species, and this plays an important role in the regulation of somatic growth and metabolism [1][2][3]. Lipolysis is stimulated by high-amplitude GH pulses, and fat accumulation occurs during continuous low GH secretion [1][2][3]. Since the Shiba goat has a distinct profile of GH pulsatility at regular intervals [4,5], it might be a good experimental model for study of the mechanisms of GH pulse generation. A previous study also demonstrated that the GH secretory pattern varies during the estrous cycle according to the changes in plasma sex steroid levels [5]. In particular, estrogen markedly enhanced the amplitude and area under the curve (AUC) of GH pulses, which has also been observed in other experiments in sheep [6,7] and baboons [8]. Therefore, lipolysis could be stimulated during the estrous phase when the GH pulses were robust. In addition, it was reported that GH release could contribute to follicular development [9] and could act as a cogonadotropin to induce ovulation [10]. Taken together, enhancement of GH pulse amplitude by estrogen may yield an appropriate metabolic milieu for the reproductive stage [1,5,11]. Nevertheless, how sex steroids ...

Levels of hormones and cytokines associated with growth in Honamlı and native hair goats

“…In the males, GHRH values increased in native hair and Honamlı goats after the 4th and 8th month, respectively. Considering the data of GH and GHRH together, it could be concluded that these parameters revealed parallel courses and they appear to correspond with those observed in previous studies (Mogi et al 2004, Yonezawa et al 2011). There were significant GHRP increases in Honamlı bucks and in the females of the both breeds after 4 months period.…”

Secretory pattern and regulatory mechanism of growth hormone in cattle

“…The research regarding GH pulsatility using Shiba goats from this group also generated additional results suggesting that GH pulses are not related to GHRH and SS but have a negative correlation with neuropeptide Y (NPY) (Yonezawa et al 2010). Furthermore, they also suggested that estrogen enhances the GH secretory pattern through stimulation of GHRH and suppression of NPY (Yonezawa et al 2011). Although we attempted to determine the relationship between two hypothalamic hormones secreted into the median eminence of the hypothalamus and peripheral GH using a push-pull perfusion system in Holstein steers, no obvious relationship among the three hormones was observed (Kasuya et al 2005).…”

“…Furthermore, they also suggested that estrogen enhances the GH secretory pattern through stimulation of GHRH and suppression of NPY (Yonezawa et al . 2011). Although we attempted to determine the relationship between two hypothalamic hormones secreted into the median eminence of the hypothalamus and peripheral GH using a push‐pull perfusion system in Holstein steers, no obvious relationship among the three hormones was observed (Kasuya et al .…”