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Modification of hypothalamic content of growth hormone regulatory peptides in maternally deprived neonatal rats
1Bowling Green State University, Biological Sciences Department, OH 43403.
Insights
Maternal deprivation in rat pups significantly increases hypothalamic growth hormone release inhibiting hormone (GHRIH). This finding may explain the known suppression of growth hormone (GH) levels observed in neonatally deprived animals.
Area of Science:
- Neuroendocrinology
- Developmental Biology
- Hormonal Regulation
Background:
- Maternal deprivation (MD) is known to suppress circulating growth hormone (GH) levels in neonatal rats.
- The hypothalamic hormones growth hormone-releasing hormone (GHRH) and GH-release-inhibiting hormone (GHRIH) regulate GH secretion.
- The impact of MD on hypothalamic GHRH and GHRIH levels remains largely uncharacterized.
Purpose of the Study:
- To investigate the effects of maternal deprivation on hypothalamic content of GHRH and GHRIH in 10-day-old rat pups.
- To determine if changes in these hypothalamic hormones correlate with the known GH suppression associated with MD.
Main Methods:
- Neonatal rat pups were subjected to maternal deprivation for 1 or 6 hours.
- Hypothalami were dissected, homogenized, and lyophilized.
- Radioimmunoassay (RIA) was used to quantify hypothalamic GHRH and GHRIH levels.
- Statistical analysis included ANOVA and Tukey's test for comparisons.
Main Results:
- A significant increase in hypothalamic GHRIH content was observed in maternally deprived rats compared to controls (P = 0.026).
- A trend towards elevated GHRIH with longer deprivation (1 vs. 6 hours) and higher levels in males was noted (P = 0.0636).
- No significant differences in hypothalamic GHRH content were found between deprived and control groups.
Conclusions:
- Neonatal maternal deprivation alters hypothalamic GHRIH levels in rat pups.
- The observed increase in GHRIH may contribute to the suppression of growth hormone release following maternal deprivation.
- This study highlights a potential neuroendocrine mechanism underlying the growth-retarding effects of early-life stress.
Abstract:
The possibility that maternal deprivation (MD) modifies growth hormone releasing hormone (GHRH) and/or growth hormone release inhibiting hormone (GHRIH) in 10-day-old rat pups was investigated by quantifying the total hypothalamic content of these two hormones which regulate the release of growth hormone (GH), since MD has previously been shown to suppress circulating GH levels. At 10 days of age, rat pups were maternally deprived for either 1 or 6 hours (control pups remained with their mother while littermates were deprived). At the end of the time period, hypothalami were dissected free, homogenized, frozen, and then lyophilized. Reconstituted extracts were later subjected to radioimmunoassay for GHRH and GHRIH. Tests for differences in the brain content of the hormones were performed by analysis of variance; multiple comparison of the means was performed using Tukey's test. A significant increase in the GHRIH content was observed in the hypothalami of maternally deprived rats as compared to control animals (P = 0.026). Small differences in the mean GHRIH content between the different experimental groups suggested a trend toward elevation of GHRIH after either 1 or 6 hours of MD and a trend toward higher levels in males as compared to females (P = 0.0636). No differences in hypothalamic GHRH content were found between maternally deprived and control pups (175.8 pg/hypothalamus vs. 171.5 pg/hypothalamus). The modification of GHRIH hypothalamic content during MD of neonatal rats demonstrated in the present study may be related to the suppression of GH that is known to result from MD.