The granin VGF promotes genesis of secretory vesicles, and regulates circulating catecholamine levels and blood pressure.

Secretion of proteins and neurotransmitters from large dense core vesicles (LDCVs) is a highly regulated process. Adrenal LDCV formation involves the granin proteins chromogranin A (CgA) and chromogranin B (CgB); CgA- and CgB-derived peptides regulate catecholamine levels and blood pressure. We investigated function of the granin VGF (nonacronymic) in LDCV formation and the regulation of catecholamine levels and blood pressure. Expression of exogenous VGF in nonendocrine NIH 3T3 fibroblasts resulted in the formation of LDCV-like structures and depolarization-induced VGF secretion. Analysis of germline VGF-knockout mouse adrenal medulla revealed decreased LDCV size in noradrenergic chromaffin cells, increased adrenal norepinephrine and epinephrine content and circulating plasma epinephrine, and decreased adrenal CgB. These neurochemical changes in VGF-knockout mice were associated with hypertension. Germline knock-in of human VGF1-615 into the mouse Vgf locus rescued the hypertensive knockout phenotype, while knock-in of a truncated human VGF1-524 that lacks several C-terminal peptides, including TLQP-21, resulted in a small but significant increase in systolic blood pressure compared to hVGF1-615 mice. Finally, acute and chronic administration of the VGF-derived peptide TLQP-21 to rodents decreased blood pressure. Our studies establish a role for VGF in adrenal LDCV formation and the regulation of catecholamine levels and blood pressure.

Effects of intrathecal kynurenate on arterial pressure during chronic osmotic stress in conscious rats.

Increased plasma osmolality elevates mean arterial pressure (MAP) through activation of the sympathetic nervous system, but the neurotransmitters released in the spinal cord to regulate MAP during osmotic stress remain unresolved. Glutamatergic neurons of the rostral ventrolateral medulla project to sympathetic preganglionic neurons in the spinal cord and are likely activated during conditions of osmotic stress; however, this has not been examined in conscious rats. This study investigated whether increased MAP during chronic osmotic stress depends on activation of spinal glutamate receptors. Rats were chronically instrumented with an indwelling intrathecal (i.t.) catheter for antagonist delivery to the spinal cord and a radiotelemetry transmitter for continuous monitoring of MAP and heart rate. Osmotic stress induced by 48 h of water deprivation (WD) increased MAP by ~15 mmHg. Intrathecal kynurenic acid, a nonspecific antagonist of ionotropic glutamate receptors, decreased MAP significantly more after 48 h of WD compared with the water-replete state. Water-deprived rats also showed a greater fall in MAP in response to i.t. 2-amino-5-phosphonovalerate. Finally, i.t. kynurenic acid also decreased MAP more in an osmotically driven model of neurogenic hypertension, the DOCA-salt rat, compared with normotensive controls. Our results suggest that spinally released glutamate mediates increased MAP during 48-h WD and DOCA-salt hypertension.

Effect of global and regional sympathetic blockade on arterial pressure during water deprivation in conscious rats.

Forty-eight hours of water deprivation (WD) in conscious rats results in a paradoxical increase in mean arterial pressure (MAP). Previous studies suggest this may be due to increased sympathetic nerve activity (SNA). However, this remains to be investigated in conscious, freely behaving animals. The purpose of this study was to determine, in conscious rats, the role of the sympathetic nervous system (SNS) in mediating WD-induced increases in MAP and to identify which vascular beds are targeted by increased SNA. Each rat was chronically instrumented with a radiotelemetry transmitter to measure MAP and heart rate (HR) and an indwelling venous catheter for plasma sampling and/or drug delivery. MAP and HR were continuously measured during a 2-day baseline period followed by 48 h of WD and then a recovery period. By the end of the WD period, MAP increased by ∼15 mmHg in control groups, whereas HR did not change significantly. Chronic blockade of α(1)/ß(1)-adrenergic receptors significantly attenuated the WD-induced increase in MAP, suggesting a role for global activation of the SNS. However, the MAP response to WD was unaffected by selective denervations of the hindlimb, renal, or splanchnic vascular beds, or by adrenal demedullation. In contrast, complete adrenalectomy (with corticosterone and aldosterone replaced) significantly attenuated the MAP response to WD in the same time frame as α(1)/ß(1)-adrenergic receptor blockade. These results suggest that, in conscious water-deprived rats, the SNS contributes to the MAP response and may be linked to release of adrenocortical hormones. Finally, this sympathetically mediated response is not dependent on increased SNA to one specific vascular bed.

Role of spinal V1a receptors in regulation of arterial pressure during acute and chronic osmotic stress.

Vasopressinergic neurons in the paraventricular nucleus project to areas in the spinal cord from which sympathetic nerves originate. This pathway is hypothesized to be involved in the regulation of mean arterial pressure (MAP), particularly under various conditions of osmotic stress. Several studies measuring sympathetic nerve activity support this hypothesis. However, the evidence that spinal vasopressin influences MAP under physiological or pathophysiological conditions in conscious animals is limited. The purpose of this study was to investigate, in conscious rats, if the increases in MAP during acute or chronic osmotic stimuli are due to activation of spinal vasopressin (V1a) receptors. Three conditions of osmotic stress were examined: acute intravenous hypertonic saline, 24- and 48-h water deprivation, and 4 wk of DOCA-salt treatment. Rats were chronically instrumented with an indwelling catheter for intrathecal injections and a radiotelemeter to measure MAP. In normotensive rats, intrathecal vasopressin and V1a agonist increased MAP, heart rate, and motor activity; these responses were blocked by pretreatment with an intrathecal V1a receptor antagonist. However, when the intrathecal V1a antagonist was given during the three conditions of osmotic stress to investigate the role of "endogenous" vasopressin, the antagonist had no effect on MAP, heart rate, or motor activity. Contrary to the hypothesis suggested by previous studies, these findings indicate that spinal V1a receptors are not required for elevations of MAP under conditions of acute or chronic osmotic stress in conscious rats.