Up-regulation of nitric oxide synthase (NOS) gene expression together with NOS activity in the rat hypothalamo-hypophysial system after chronic salt loading: evidence of a neuromodulatory role of nitric oxide in arginine vasopressin and oxytocin secretion.

Abstract

Chronic salt loading up-regulated the expression of neuronal nitric oxide synthase (NOS) mRNA in the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus with a concomitant increase in NOS activity in the posterior pituitary. Once daily ip injection of N-omega-nitroarginine (N-Arg), a NOS inhibitor, significantly inhibited NOS activity in the posterior pituitary in a dose-dependent manner, but did not influence NOS mRNA levels. Two percent salt loading for 3 or 4 days significantly depleted the contents of both arginine vasopressin (AVP) and oxytocin (OT) in the posterior pituitary, and simultaneous treatment with daily injections of N-Arg at a dose of 10 mg/kg significantly enhanced the depletion of both AVP and OT. This effect was dose dependent and paralleled the inhibition of NOS activity in the posterior pituitary. N-Arg treatment had no effect on the levels of both AVP and OT transcripts in PVN or SON. These results suggest that NOS gene expression in the SON and PVN of the rat hypothalamus is increased during hyperosmotic stimulation and suggest a neuromodulatory role for NO in the rat hypothalamo-hypophysial system as an inhibitory regulator of AVP and OT secretion.

Permanently compromised NADPH-diaphorase activity within the osmotically activated supraoptic nucleus after in utero but not adult exposure to Aroclor 1254

“…The NADPH-diaphorase (NADPH-d) enzyme activity that is associated with NOS activity sustains routine fixation procedures with aldehydes and has been used as a reliable indicator of NOS enzymatic activity in paraformaldehyde-fixed brain tissue including the SON (Kadowaki et al, 1994;Matsumoto et al, 1993;Villar et al, 1994). In agreement with others, we found that hyperosmotic stimulation of early and late adulthood rats triggered an activitydependent increase in NADPH-d staining density in the SON (Soinila et al, 1999;Yun et al, 2005).…”

“…NO has been described as an activity-dependent modulator of the magnocellular neurosecretory system. We and others have shown that NO signaling is required for stimulated VP release from SON tissue punches (Gillard et al, 2007) and the latter serves to regulate MNC electrical activity and pituitary VP output (Kadowaki et al, 1994;Liu et al, 1998;Stern and Ludwig, 2001;Stern and Zhang, 2005). Moreover, nNOS expression and NOS activity (as assessed by NADPH-d) in MNCs appears to be responsive to physiological state, suggesting an activity-dependent role for NO signaling in the control of body water and salt balance.…”

“…NADPH is a required cofactor for NOS enzyme activity (Dawson et al, 1991) and NOS has NADPH-d activity (Hope et al, 1991). An enhancement of NADPH-d staining in fixed sections coincides with a respective rise in the amount of NOS protein (Kishimoto et al, 1996) and NOS gene expression (Kadowaki et al, 1994); therefore, NAPDH-d staining can be used as an indicator of NOS activity in paraformaldehyde-fixed tissue (Matsumoto et al, 1993;Young et al, 1997). Our data indicate that early developmental PCB exposure significantly compromises NOS responses to osmotic activation in the adult supraoptic nucleus, an effect which may lead to PCB-induced disruption of neuroendocrine function and osmoregulation.…”

Nitric oxide synthase and background adaptation in Xenopus laevis

“…Further research will be necessary to localize the NOergic neurons in higher brain centers that innervate the PI of Xenopus lae6is and to investigate the NOergic input of the PI via fibers running through the median eminence. These fibers may appear similar to the NOergic nerve endings found in the mammalian PN (Kadowaki et al, 1994;Pow, 1994;Vanhatalo and Soinila, 1995), although due attention should be paid to the difference in pituitary innervation between mammals and amphibians. Also in analogy with the mammalian pituitary, a local (paracrine or autocrine) effect of NO in the PN (Pow, 1994) and the PI ( Vanhatalo and Soinila, 1995) cannot be excluded, but requires further studies.…”

Postnatal Development of NADPH-Diaphorase Activity in the Rat. The Role of Nitric Oxide in the Ontogeny of Arginine Vasopression and Oxytocin.

“…It was reported that NOS mRNA and NADPH-d activity are upregulated in response to salt loading [17,38,39] or hypotension [40]. Stimulatory action was augmented by inhibitors of NO formation, suggesting that endogenous NO has an inhibitory effect on the release of these peptides [30,34,35].…”