Increased angiotensin-(1-7) in hypophysial-portal plasma of conscious sheep.
Studies were undertaken to characterize angiotensin peptides in hypophysial-portal blood of conscious sheep and to determine whether the median eminence (ME) secretes angiotensin peptides into the hypophysial-portal circulation. Simultaneous measurements of angiotensin peptides in jugular and hypophysial-portal plasma were performed in 6 sheep. Cerebrospinal fluid (CSF) was collected and data for hypophysial-portal plasma were corrected for CSF contamination. Angiotensin peptides were also measured in extracts of sheep ME. In a separate group of 4 sheep, simultaneous measurements of angiotensin peptides in arterial and jugular plasma were performed. Using high performance liquid chromatography-based radioimmunoassays, 8 angiotensin peptides were measured: Ang-(1-7), Ang II, Ang-(1-9), Ang I, Ang-(2-7), Ang III, Ang-(2-9), and Ang-(2-10). Renin, angiotensinogen and prolyl endopeptidase were also measured. No differences in angiotensin peptide levels in arterial and jugular plasma were observed. Angiotensin peptide levels in hypophysial-portal plasma were similar to those in jugular plasma, except for Ang-(1-7), the levels of which were 5-fold higher in hypophysial-portal plasma, and Ang I, for which the levels in hypophysial-portal plasma were 46% of the jugular levels. Renin and angiotensinogen levels were similar in arterial, jugular, and hypophysial-portal plasma. Angiotensin peptide contents of sheep ME were less than 16 fmol/ME. However, the prolyl endopeptidase content of sheep ME was 430-fold higher than plasma levels. The low levels of angiotensin peptides in sheep ME indicate that it does not secrete these peptides into the hypophysial-portal circulation. Rather, the high level of prolyl endopeptidase in ME is consistent with region-specific metabolism of Ang I delivered to the ME by arterial blood, generating increased levels of Ang-(1-7) in hypophysial portal plasma. The increased levels of Ang-(1-7) in hypophysial-portal plasma may play a role in regulation of pituitary function.
Lawrence
A C
AC
St. Vincent's Institute of Medical Research, Fitzroy, Australia.
Clark
I J
IJ
Campbell
D J
DJ
D000803:Angiotensin I; D000804:Angiotensin II / Q000097:blood* / Q000134:cerebrospinal fluid; D000808:Angiotensinogen / Q000097:blood / Q000134:cerebrospinal fluid; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D010450:Endopeptidases / Q000097:blood / Q000134:cerebrospinal fluid; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism; D008473:Median Eminence / Q000378:metabolism*; D010446:Peptide Fragments / Q000097:blood* / Q000134:cerebrospinal fluid; D010455:Peptides / Q000097:blood / Q000134:cerebrospinal fluid; D010902:Pituitary Gland / Q000098:blood supply*; D011168:Portal System / Q000378:metabolism*; D000085822:Prolyl Oligopeptidases; D011863:Radioimmunoassay; D012083:Renin / Q000097:blood / Q000134:cerebrospinal fluid; D012697:Serine Endopeptidases; D012756:Sheep
D010446:Peptide Fragments; D010455:Peptides; D000808:Angiotensinogen; D000804:Angiotensin II; D007987:Gonadotropin-Releasing Hormone; D000803:Angiotensin I; D010450:Endopeptidases; D012697:Serine Endopeptidases; D000085822:Prolyl Oligopeptidases; D012083:Renin; C118790:angiotensin I (1-7)