+ Site Statistics
+ Search Articles
+ PDF Full Text Service
How our service works
Request PDF Full Text
+ Follow Us
Follow on Facebook
Follow on Twitter
Follow on LinkedIn
+ Subscribe to Site Feeds
Most Shared
PDF Full Text
+ Translate
+ Recently Requested

Photoperiodic control of growth hormone secretion and body weight in rams

Photoperiodic control of growth hormone secretion and body weight in rams

Domestic Animal Endocrinology 5(3): 247-256

This study was undertaken to assess the influence of photoperiod on growth hormone (GH) secretion in rams and its possible influence on body weight. Twenty young adult rams were divided into two groups. One was subjected to an annual (AR) and the other to a semestral (SR) light regime during the same 18-month period. In both groups, daylength (DL) varied gradually between 8 to 17 hr. Plasma prolactin (PRL) and GH profiles consisting of 6 hr samples were determined and animals were weighed throughout the course of the experiment. Maximal PRL secretion was observed with largest DL. In contrast, GH secretion increased during increasing DL but it began to decrease before maximal DL was reached in both light regimes. Mean GH secretion was maximal when the DL was about 11 hr in SR and between 8 to 12 hr in AR. Similarly, body weight increased when DL increased and plateaued during decreasing DL in both AR and SR animal groups. Significant (P < 0.05) differences were observed throughout the course of the experiment according to the effects of decreasing or increasing DL in each group. Analysis of variance showed that the effect of DL on plasma PRL and GH levels and weight velocity (WV) was significant (P < 0.05) in both light regimes. This suggests that in SR, plasma PRL and GH levels and WV vary according to a six month period. Estimation of the lag times between DL and GH or WV indicated that maximal plasma GH levels and WV preceded maximal DL by about 45 and 18 days, respectively, and that there was a delay of about 27 days between photoperiod-induced GH and WV changes. In contrast, there was no lag time between DL and PRL. Therefore there was a lag time of 45 days between maximal levels of GH and PRL. These findings indicate that variations in GH secretion and body weight are related to similar photoperiodic stimuli and suggest that GH could be involved in mediating the growth-promoting effect of increasing photoperiod.

Please choose payment method:

(PDF emailed within 0-6 h: $19.90)

Accession: 001654409

Download citation: RISBibTeXText

PMID: 3224525

DOI: 10.1016/0739-7240(88)90036-7

Related references

Relationships between some estimates of growth hormone and prolactin secretion and rates of accretion of constituents of body gain in rams. Animal Production 41(1): 103-111, 1985

Role endogenous opioids in the photoperiodic control of pulsatile lh secretion in rams. Neuroscience Letters Suppl. (29): S44, 1987

A novel growth hormone secretagogue-1a receptor antagonist that blocks ghrelin-induced growth hormone secretion but induces increased body weight gain. Neuroendocrinology 81(5): 339-349, 2005

The effect of diet and reduced body weight on plasma glucose concentration insulin c peptide glucagon growth hormone and cortisol secretion in over weight newly detected diabetics. Diabetologia Croatica 10(Suppl. 1): 5-6, 1981

Effect of immunisation against growth hormone-releasing hormone on body composition and wool growth in Merino rams fed two levels of nutrition. Asian-Australasian Journal of Animal Sciences 13(Suppl. Vol B): 34-38, 2000

Reduced growth hormone secretion in Turner syndrome: is body weight a key factor?. Hormone Research 41(1): 27-32, 1994

Altered 24-hour growth hormone secretion/insulin-like growth factor-I axis in obesity An acquired defect reversed with body weight loss. International Journal of Obesity 18(Suppl. 2): 165, 1994

Somatomedin activity and growth hormone secretion 1. changes related to body weight in anorexia nervosa. Acta Paediatrica Scandinavica 69(1): 37-42, 1980

Photoperiodic control of thyroid function and wool and horn growth in rams and the effect of cranial sympathectomy. Endocrinology 107(5): 1543-1548, 1980

Response of body weight and clearance and secretion rates of growth hormone to photoperiod in Holstein heifers. Journal of Animal Science 62(5): 1273-1278, 1986

Growth characteristics of metallothionein human growth hormone transgenic mice as compared to mice selected for high eight week body weight and unselected controls i. body weight gain and external body dimensions. Growth Development and Aging 55(4): 225-235, 1991

Acute changes in growth hormone-releasing hormone secretion after injection of BIM 23014, a long acting somatostatin analog, in rams. Life Sciences 51(11): 831-838, 1992

Seasonal reproduction in rams: influence of natural photoperiod on scrotal circumference, sexual flush, body weight and body condition score in mature F2 Finnish Landrace X Dorset rams. Sheep Research Journal 5(3): 14-17, 1989