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ABSTRACT
The effect of six hypothalamic peptides on the basal release of ACTH and that induced by arginine vasopressin (AVP) or by ovine corticotrophin releasing factor (oCRF) from fragments of the rat anterior pituitary gland incubated in vitro was investigated. Dose–response curves to AVP and to oCRF were obtained, and the response to a low dose of oCRF was potentiated by a low dose of AVP. Basal release of ACTH was not affected by any of the peptides in concentrations in the range 10−12 to 10−6 mol/l, and only substance P (SP) and somatostatin (SRIF) inhibited significantly the response to oCRF in a dose-related manner. The responses to a range of doses of oCRF or AVP were reduced by 10−8 and 10 − 6 mol SP or SRIF/1, and to a greater extent by the higher dose. Except in the case of 10−6 mol SRIF/1 on the response to AVP, the response was not further diminished by preincubation of the tissue with the peptide before the stimulating agent was added. The inhibition of the responses to AVP or oCRF by 10−9 mol SP/1 was not potentiated by its combination with either 5 × 10−10 or 10−8 mol SRIF/1; the inhibitory effects were merely additive. The results suggest that although SRIF and SP are able to modulate the release of ACTH from the anterior pituitary gland, they do so only at a high concentration. In the case of SRIF these concentrations are several orders of magnitude higher than those reported to be present in the hypophysial portal blood and therefore a physiological role for this peptide in the control of ACTH secretion is unlikely.
J. Endocr. (1984) 100, 219–226
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ABSTRACT
Peptide YY (PYY), a thirty-six amino acid intestinal hormonal peptide with a tyrosine residue at each end (hence YY as Y represents tyrosine in the new peptide nomenclature), was found throughout the gastrointestinal tract of the pig. Concentrations were very low in the foregut (antrum, 3·4 ± 0·3 pmol/g; duodenum, 1·1 ± 1·5 pmol/g), higher in the distal small intestine (ileum, 100 ± 13 pmol/g) and very high in the large bowel (descending colon, 270 ± 45 pmol/g).
Peptide YY was found to circulate in plasma and concentrations rose substantially in response to eating (fasting, 138 ± 15 pmol/l; postprandial, 263 ± 21 pmol/l; P<0·001). There was a small but significant portal/arterial gradient in postprandial PYY levels.
More than 90% of the immunoreactive PYY in gut extracts eluted, on gel permeation chromatography, in an identical position to pure PYY standard, but small amounts of higher molecular weight material, possibly precursors, were detected. In contrast, plasma from fasting pigs contained a large proportion (60–70%) of these large molecular forms. These findings suggest that the putative pro-PYY may be cleared more slowly from the circulation than the 36 amino acid hormonal peptide.
The high concentrations of immunoreactive PYY in the circulation of the young pig may reflect a species difference between pig and man or may indicate an important role for PYY in the developing animal.
J. Endocr. (1987) 113, 11–14
