Pulsatile growth hormone secretion during the breeding season in male reindeer and its association with hypophagia and weight loss.
Male deer reduce food intake and lose weight during the breeding season (rut) in autumn. Growth hormone (GH) is lipolytic in ruminants; therefore, pulsatile GH secretion was measured in three young reindeer (Rangifer tarandus tarandus) bulls during the natural period of weight loss during rut. Blood samples were withdrawn through a jugular cannula every 20 min for 16 hr on 5 occasions from late summer to early winter in unanaesthetised animals. The deer were group fed a pelleted concentrate ration ad libitum, and food intake, body weight, and testicular diameter were recorded. The hormone profiles were analysed by the pulse detection algorithm PULSAR. The bulls showed the normal pattern of rut-associated weight loss and reduced food intake followed by a period of weight increase in late autumn before weight plateaued in early winter. Mean GH was highest (P less than 0.05) at the time of minimum body weight and food intake compared with all other sampling periods. Neither the amplitude nor the frequency of GH pulses, as detected by PULSAR, differed significantly with sampling period, although the high mean GH values were associated with a different pulse shape; pulses were longer, with a large area under the curve, presumably reflecting a longer duration of secretion or reduced clearance. Thus weight loss and low food intake were associated with long, large area pulses of GH. An opioid antagonist, naloxone, was given to reindeer intravenously at hourly intervals for 4 hr and blood sampling was continued for 7 hr.(ABSTRACT TRUNCATED AT 250 WORDS)
Suttie
J M
JM
Institute of Arctic Biology, University of Alaska, Fairbanks 99775.
White
R G
RG
Littlejohn
R P
RP
D000704:Analysis of Variance; D000818:Animals; D004435:Eating; D013006:Growth Hormone / Q000378:metabolism*; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D010507:Periodicity; D012053:Reindeer / Q000502:physiology*; D013737:Testis / Q000033:anatomy & histology; D015431:Weight Loss
D009270:Naloxone; D013006:Growth Hormone