From Newborn to Senescence Morphological and Functional Remodeling Leads to Increased Contractile Capacity of Arteries

VPAC1 receptors play a dominant role in PACAP-induced vasorelaxation in female mice

Background

PACAP and VIP are closely related neuropeptides with wide distribution and potent effect in the vasculature. We previously reported vasomotor activity in peripheral vasculature of male wild type (WT) and PACAP-deficient (KO) mice. However, female vascular responses are still unexplored. We hypothesized that PACAP-like activity is maintained in female PACAP KO mice and the mechanism through which it is regulated differs from that of male PACAP KO animals.

Methods

We investigated the vasomotor effects of VIP and PACAP isoforms and their selective blockers in WT and PACAP KO female mice in carotid and femoral arteries. The expression and level of different PACAP receptors in the vessels were measured by RT-PCR and Western blot.

Results

In both carotid and femoral arteries of WT mice, PACAP1-38, PACAP1-27 or VIP induced relaxation, without pronounced differences between them. Reduced relaxation was recorded only in the carotid arteries of KO mice as compared to their WT controls. The specific VPAC1R antagonist completely blocked the PACAP/VIP-induced relaxation in both arteries of all mice, while PAC1R antagonist affected relaxation only in their femoral arteries.

Conclusion

In female WT mice, VPAC1 receptors appear to play a dominant role in PACAP-induced vasorelaxation both in carotid and in femoral arteries. In the PACAP KO group PAC1R activation exerts vasorelaxation in the femoral arteries but in carotid arteries there is no significant effect of the activation of this receptor. In the background of this regional difference, decreased PAC1R and increased VPAC1R availability in the carotid arteries was found.

Remodeling of Wall Mechanics and the Myogenic Mechanism of Rat Intramural Coronary Arterioles in Response to a Short-Term Daily Exercise Program: Role of Endothelial Factors

PURPOSE

Exercise elicits early adaptation of coronary vessels enabling the coronary circulation to respond adequately to higher flow demands. We hypothesized that short-term daily exercise induces biomechanical and functional remodeling of the coronary resistance arteries related to pressure.

METHODS

Male rats were subjected to a progressively increasing 4-week treadmill exercise program (over 60 min/day, 1 mph in the final step). In vitro pressure-diameter measurements were performed on coronary segments (119 ± 5 μm in diameter at 50 mm Hg) with microarteriography. The magnitude of the myogenic response and contribution of endogenous nitric oxide and prostanoid production to the wall mechanics and pressure-diameter relationship were assessed.

RESULTS

Arterioles isolated from exercised ani mals - compared to the sedentary group - had thicker walls, increased distensibility, and a decreased elastic modulus as a result of reduced wall stress in the low pressure range. The arterioles of exercised rats exhibited a more powerful myogenic response and less endogenous vasoconstrictor prostanoid modulation at higher pressures, while vasodilator nitric oxide modulation of diameter was augmented at low pressures (< 60 mm Hg).

CONCLUSIONS

A short-term daily exercise program induces remodeling of rat intramural coronary arterioles, likely resulting in a greater range of coronary autoregulatory function (constrictor and dilator reserves) and more effective protection against great changes in intraluminal pressure, contributing thereby to the optimization of coronary blood flow during exercise.

Aging-Induced Modulation of Pituitary Adenylate Cyclase-Activating Peptide- and Vasoactive Intestinal Peptide-Induced Vasomotor Responses in the Arteries of Mice

Pituitary adenylate cyclase-activating peptide (PACAP; 1-38 and 1-27) and vasoactive intestinal peptide (VIP) are related neuropeptides of the secretin/glucagon family. Overlapping signaling through G-protein-coupled receptors mediates their vasomotor activity. We previously showed that PACAP deficiency (PACAP-KO) shifts the mechanisms of vascular response and maintains arterial relaxation through the VIP backup mechanism and (mainly) its VPAC1R, but their age-dependent modulation is still unknown. We hypothesized that backup mechanisms exist, which maintain the vasomotor activity of these peptides also in older age. Thus, we investigated the effects of exogenous VIP and PACAP peptides in isolated carotid arteries of 2- and 15-month-old wild-type (WT) and PACAP-KO mice. All peptides induced relaxation in the arteries of young WT mice, whereas in young PACAP-KO mice PACAP1-27 and VIP, but not PACAP1-38, induced relaxation. Unlike VIP, PACAP-induced vasomotor responses were reduced in aging WT mice. However, in the arteries of aging PACAP-KO mice, PACAP1-27- and VIP-induced responses were reduced, but PACAP1-38 showed a greater vasomotor response compared to that of young PACAP-KO animals. There were no significant differences between the vasomotor responses of aging WT and PACAP-KO mice. Our data suggest that, in the absence of PACAP both in young and old ages, the vascular response is mediated through backup mechanisms, most likely VIP, maintaining proper vascular relaxation in aging-induced PACAP insufficiency.

Backup Mechanisms Maintain PACAP/VIP-Induced Arterial Relaxations in Pituitary Adenylate Cyclase-Activating Polypeptide-Deficient Mice

BACKGROUND

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a multifunctional neuropeptide in the VIP/secretin/glucagon peptide superfamily. Two active forms, PACAP1-38 and PACAP1-27, act through G protein-coupled receptors, the PAC1 and VPAC1/2 receptors. Effects of PACAP include potent vasomotor activity. Vasomotor activity and organ-specific vasomotor effects of PACAP-deficient mice have not yet been investigated; thus, the assessment of its physiological importance in vasomotor functions is still missing. We hypothesized that backup mechanisms exist to maintain PACAP pathway activity in PACAP knockout (KO) mice. Thus, we investigated the vasomotor effects of exogenous vasoactive intestinal peptide (VIP) and PACAP polypeptides in PACAP wild-type (WT) and PACAP-deficient (KO) male mice.

METHODS

Carotid and femoral arteries were isolated from 8- to 12-week-old male WT and PACAP-KO mice. Vasomotor responses were measured with isometric myography.

RESULTS

In the arteries of WT mice the peptides induced relaxations, which were significantly greater to PACAP1-38 than to PACAP1-27 and VIP. In KO mice, PACAP1-38 did not elicit relaxation, whereas PACAP1-27 and VIP elicited significantly greater relaxation in KO mice than in WT mice. The specific PAC1R and VPAC1R antagonist completely blocked the PACAP-induced relaxations.

CONCLUSION

Our data suggest that in PACAP deficiency, backup mechanisms maintain arterial relaxations to polypeptides, indicating an important physiological role for the PACAP pathway in the regulation of vascular tone.