Angiotensin reactivity in the cheek pouch of the renovascular hypertensive hamster

Role of mast cell chymase in angiotensin-induced vascular contraction of hamster cheek pouch microvessels

We investigated the contribution of chymase-dependent conversion of angiotensin I to angiotensin II in hamster cheek pouch. To investigate the converting activities in intact tissues, angiotensin I or II was applied to microvessels of the intact cheek pouch, and the vascular contractile response was recorded. Angiotensin I or angiotensin II (20 nM) induced a rapid contraction of arterioles, irrespective of their diameter. In the presence of I mM captopril, there was no contraction in response to angiotensin I in arterioles < 25 microm in diameter, whereas contraction was still observed in larger arterioles. Chymostatin (100 microM) treatment also reduced the response to angiotensin I in arterioles > 40 microm in diameter. Treatment with 1 mM captopril and 100 microM chymostatin resulted in the loss of response to angiotensin I, but not to angiotensin II, in all arterioles. Treatment of microvessels with 100 microg/ml compound 48/80 enhanced angiotensin I-induced vascular contraction response, suggesting the significance of mast cells as a source of cheek pouch chymase.

Liposomal VIP attenuates phenylephrine- and ANG II-induced vasoconstriction in vivo

The purpose of this study was to determine whether vasoactive intestinal peptide (VIP) modulates vasoconstriction elicited by phenylephrine and ANG II in vivo and, if so, to begin to elucidate the mechanisms underlying this phenomenon. Using intravital microscopy, we found that suffusion of phenylephrine and ANG II elicits significant vasoconstriction in the in situ hamster cheek pouch that is potentiated by VIP-(10-28), a VIP receptor antagonist, but not by VIP-(1-12) (P < 0.05). Aqueous VIP has no significant effects on phenylephrine- and ANG II-induced vasoconstriction. However, VIP on sterically stabilized liposomes (SSL), a formulation where VIP assumes a predominantly alpha-helix conformation, significantly attenuates this response. Maximal effect is observed within 30 min and is no longer seen after 60 min. Empty SSL are inactive. Indomethacin has no significant effects on responses induced by VIP on SSL. The vasodilators ACh, nitroglycerin, calcium ionophore A-23187, 8-bromo-cAMP, and isoproterenol have no significant effects on phenylephrine- and ANG II-induced vasoconstriction. Collectively, these data suggest that vasoconstriction modulates VIP release in the in situ hamster cheek pouch and that alpha-helix VIP opposes alpha-adrenergic- and ANG II-induced vasoconstriction in this organ in a reversible, prostaglandin-, NO-, cGMP-, and cAMP-independent fashion.

Local renin-angiotensin system in the microcirculation of spontaneously hypertensive rats

We studied the local renin-angiotensin system in the microcirculation of cremaster muscle in spontaneously hypertensive rats (SHR) and their normotensive Wistar-Kyoto (WKY) controls. We used intravital microscopy in an original preparation of cremaster isolated from its normal blood supply and externally perfused with physiological solution, thus allowing the exclusion of circulating converting enzyme, circulating renin, and circulating angiotensinogen. We classified arterioles studied as second-, third-, and fourth-order, with mean diameters, respectively, of 67 +/- 6, 35 +/- 2, and 17 +/- 1 microns in WKY controls and 61 +/- 5, 34 +/- 2, and 16 +/- 1 microns in SHR. No difference between WKY controls and SHR was found for arteriolar vasoconstrictions in response to topical administration of 0.01 to 1 nmol/mL angiotensin II. Conversely, in response to 0.01 to 1 nmol/mL angiotensin I, significantly more arteriolar vasoconstriction was found in SHR cremaster muscle. In both strains, responses to angiotensin I were significantly inhibited by 10 nmol/mL of the angiotensin-converting enzyme inhibitor lisinopril. When angiotensinogen-rich, renin-free plasma containing 2.3 nmol/mL angiotensinogen was administered, almost no vasoconstriction was found in WKY controls, but significant constrictions were observed in SHR (23 +/- 4%, 30 +/- 5%, and 41 +/- 4% for second-, third-, and fourth-order arterioles, respectively). In SHR, vasoconstriction in response to angiotensinogen-rich, renin-free plasma was dose dependent, was inhibited by lisinopril, and was not found 24 hours after bilateral nephrectomy. Topical administration of 1.2 micrograms/mL renin did not induce arteriolar vasoconstriction in either WKY or SHR cremaster muscle.(ABSTRACT TRUNCATED AT 250 WORDS)