Does tyrosine act as a nutritional signal mediating the effects of increased feed intake on luteinizing hormone patterns in growth-restricted lambs?
We tested the hypothesis that the increase in LH secretion associated with elevated feed intake in nutritionally growth-restricted lambs is due to increased availability of tyrosine (TYR). Ovariectomized ewe lambs with abomasal cannulae were fed a complete diet in amounts (0.6 Mcal of net energy/day) sufficient to maintain a body weight of 21.7 +/- 1.0 kg between 10 and 32 wk of age. At 32 wk of age, lambs were assigned at random to one of three treatments: 1) maintenance feeding + abomasal infusion of water (M; n = 6); 2) maintenance feeding + abomasal infusion of TYR (M + TYR; n = 7); or 3) twice maintenance feeding + abomasal infusion of water (TM; n = 6). TYR (1.25 g/100 ml water) or water (100 ml) was delivered as a bolus injection at 0600, 1200, 1800, and 2400 h daily for 23 days. Plasma concentrations of TYR 10 and 22 days after initiation of treatments were higher (p less than 0.001) in the TM and M + TYR groups compared to the M group and were elevated (p less than 0.001) in the M + TYR group compared to the TM group. Concentrations of TYR in hypothalami were higher (p less than 0.01) in the M + TYR and TM groups than in the M group, and greater (p less than 0.005) in the M + TYR group compared to the TM group. Overall, there was a linear (p less than 0.001) correlation between plasma and hypothalamic concentrations of TYR.(ABSTRACT TRUNCATED AT 250 WORDS)
Hall
J B
JB
Department of Animal Sciences, University of Kentucky, Lexington 40546-0215.
Schillo
K K
KK
Hileman
S M
SM
Boling
J A
JA
D000818:Animals; D004305:Dose-Response Relationship, Drug; D004435:Eating / Q000187:drug effects* / Q000502:physiology; D005260:Female; D006130:Growth Disorders / Q000097:blood* / Q000503:physiopathology; D007031:Hypothalamus / Q000737:chemistry / Q000187:drug effects; D007986:Luteinizing Hormone / Q000097:blood*; D010052:Ovariectomy; D011863:Radioimmunoassay; D012756:Sheep / Q000502:physiology*; D014443:Tyrosine / Q000032:analysis / Q000097:blood / Q000494:pharmacology*
D014443:Tyrosine; D007986:Luteinizing Hormone