Synergism and diurnal variations of human growth hormone-releasing factor (1-29)NH2 and thyrotropin-releasing factor on growth hormone release in dairy calves.
Sixteen male Holstein calves averaging 168 kg body weight (BW) were used to determine the effects of human growth hormone-releasing factor (1-29)NH2 (hGRF (1-29)NH2; .22 micrograms/kg BW), thyrotropin-releasing factor (TRF; .165 micrograms/kg BW) or hGRF (1-29)NH2 plus TRF (.22 and .165 micrograms/kg BW, respectively) on growth hormone (GH) release in animals exposed to 16 hr of light (L): 8 hr of dark (D) (lights on at 0100 hr) and hGRF plus TRF (.22 and .165 micrograms/kg BW, respectively) in animals exposed to 8L:16D (lights on at 0900 hr). For each treatment, times of iv injection were 0400, 1000, 1600 and 2200 hr. In animals exposed to 16L:8D, average GH peaks reached after hGRF (1-29)NH2 or TRF injections were 49.7 and 32.0 ng/ml while the area under the GH response curve (AUC) were 1247 and 1019 ng/ml.min, respectively. There was no significant effect of times of injection on GH release following the separate injection of hGRF(1-29)NH2 or TRF. In animals exposed to 16L:8D, GH peaks and AUC after hGRF plus TRF injections were 226.4, 189.2 and 116.8 ng/ml, and 4340, 3660 and 2415 ng/ml.min at 0400, 1000 and 1600 hr (lights on), respectively but only 42.3 ng/ml and 1692 ng/ml.min at 2200 hr (lights off). In animals exposed to 8L:16D, GH levels and AUC after hGRF plus TRF injections reached 177.5 and 180.5 ng/ml, and 2759 and 3704 ng/ml.min at 1000 and 1600 hr (lights on) but only 84.0 and 72.7 ng/ml, and 1544 and 1501 ng/ml.min at 0400 and 2200 hr (lights off), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Lapierre
H
H
Agriculture Canada, Lennoxville, Quebec.
Petitclerc
D
D
Pelletier
G
G
Dubreuil
P
P
Morisset
J
J
Gaudreau
P
P
Couture
Y
Y
Brazeau
P
P
D000818:Animals; D002417:Cattle / Q000502:physiology*; D013006:Growth Hormone / Q000097:blood / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D007275:Injections, Intravenous; D008027:Light; D008297:Male; D010446:Peptide Fragments / Q000008:administration & dosage / Q000494:pharmacology*; D010507:Periodicity; D017337:Sermorelin; D013973:Thyrotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D013997:Time Factors
D010446:Peptide Fragments; D013973:Thyrotropin-Releasing Hormone; D017337:Sermorelin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone