Effect of Protein Deficiency on Luteinizing Hormone Releasing Hormone (LHRH), Gonadotropin Releasing Hormone Associated Peptide (GAP) and Luteinizing Hormone (LH) Immunocytochemistry in the Hypothalamus and Pituitary Gland of Prepubertal Ewes

 

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Summary

Growing female lambs were fed diets containing 14.2% (standard) or 8.1% (protein restricted) of proteins to determine their effects on puberty and luteinizing hormone releasing hormone (LHRH), gonadotropin hormone associated peptide (GAP), luteinizing hormone (LH) hormonal system. At the end of the experiment (30-34 weeks of age), hypothalamic LHRH, GAP and pituitary LH were analysed by immunocytochemical methods using specific antibodies. Plasma LH were determined by radioimmunoassay at 21 weeks of age. It was found that lowering of the dietary proteins content decreased the concentration of basal plasma LH significantly in lambs of 21 weeks of age. None of the sheep of this group reached sexual maturity at the same time as the animals of the standard group. However, immunoreactive (ir) LHRH neuronal system of protein restricted lambs was normally developed: Numerous irLHRH perikarya, dense network of axons and abundant material stored in the nerve terminals were well visualized in the typical sites of the preoptico-septal area, hypothalamus and the median eminence (ME). Gonadotropin associated peptide (GAP) of the LHRH precursor was present in the same populations of neurons that contained LHRH in the sheep brain. The proportion of pituitary LH-cells was three fold higher in pituitaries of the nutritionally restricted group. They displayed hypertrophy and very strong immunoreaction. These results show that protein deficiency in diets of growing female sheep delays their puberty but does not impair the synthesis and processing of LHRH in the brain neurons and synthesis of LH in pituitary cells. It is suggested, that the restriction of protein in diets of growing female lambs delays the appearance of first ovulation probably due to changes in the neural mechanism responsible for the preovulatory LHRH/LH output.