The effect of water deprivation on signalling molecules that utilise cGMP in the spinifex hopping mouse Notomys alexis.

Abstract

In mammals the natriuretic and guanylin peptides influence renal and intestinal fluid content and electrolyte transport by binding to and activating guanylyl cyclase (GC) receptors that in turn stimulate production of the intracellular second messenger guanosine 3?:5?-cyclic monophospate (cGMP). However, the role of natriuretic and guanylin peptides in desert mammals is not understood. The spinifex hopping-mouse (Notomys alexis), has a suite of behavioural and physiological mechanisms that permits survival for extended periods without access to free water. Because signalling molecules that generate cGMP are known to promote water excretion, it was predicted that natriuretic and guanylin peptide synthesis would be down regulated in water-deprived N. alexis, and thus reduce the amount of water lost in the urine and faeces. However, in the kidney ANP and GC-A mRNA levels were increased in water-deprived mice, but CNP and GC-B mRNA levels were decreased. Water deprivation increased guanylin and uroguanylin mRNA expression in the distal colon, but it remained unchanged in the kidney and proximal colon. The expression of GC-C mRNA increased in the proximal colon but not in the distal colon. This study shows that water deprivation differentially affects the expression of regulatory molecules that stimulate cGMP production, and that a down-regulation associated with water conservation does not uniformly occur.

Endocrinology of osmoregulation and thermoregulation of Australian desert tetrapods: A historical perspective

“…This finding, for the mammalian species with the most extreme urinary concentrating ability, adds strong support to the general consensus that desert rodents do not rely on increased AVP to survive chronic water deprivation, despite desert species having overall higher AVP levels than non-desert species (Heimeier et al 2004;Heimeier and Donald 2006;Weaver et al 1994). utilise the secondary messenger cGMP to mediate the action of NPs, via guanylyl cyclase activity (Heimeier and Donald 2006;Heimeier et al 2002Heimeier et al , 2004. In the absence of a clear role for AVP in allowing spinifex hopping mice to survive chronic water deprivation, Heimeier et al (2002Heimeier et al ( , 2004 examined the response of the NP system of water-deprived hopping mice to determine if this antagonistic endocrine system contributed to their renal response.…”

“…It appears that hopping mice require a week to acclimate to chronic water deprivation, but after this period they re-adjust their osmotic balance and as their plasma osmolarity and water volume return to normal they no longer stimulate vasopressin and natriuretic peptide responses. This finding, for the mammalian species with the most extreme urinary concentrating ability, adds strong support to the general consensus that desert rodents do not rely on increased AVP to survive chronic water deprivation, despite desert species having overall higher AVP levels than non-desert species (Heimeier et al 2004;Heimeier and Donald 2006;Weaver et al 1994). utilise the secondary messenger cGMP to mediate the action of NPs, via guanylyl cyclase activity (Heimeier and Donald 2006;Heimeier et al 2002Heimeier et al , 2004.…”

“…These effects varied with the period of water deprivation; atrial NP mRNA and guanylyl cyclase mRNA increased in the kidney after seven days of water deprivation and atrial NP mRNA decreased after 14 days while guanylyl cyclase mRNA returned to control levels (Heimeir et al 2002(Heimeir et al , 2004. A more comprehensive analysis of the NP system of hopping mice examined plasma levels of atrial and c-type NPs, mRNA expression of both these NPs and the three receptors, and renal NP receptor guanylyl cyclase activity, for water deprivation periods of three, seven, 14 and 28 days (Heimeier et al 2004). There was no uniform down-regulation of these factors during the experimental period, as might be expected for water conservation.…”

“…utilise the secondary messenger cGMP to mediate the action of NPs, via guanylyl cyclase activity (Heimeier and Donald 2006;Heimeier et al 2002Heimeier et al , 2004. In the absence of a clear role for AVP in allowing spinifex hopping mice to survive chronic water deprivation, Heimeier et al (2002Heimeier et al ( , 2004 examined the response of the NP system of water-deprived hopping mice to determine if this antagonistic endocrine system contributed to their renal response. They found that renal atrial NP played a more important role than cardiac atrial NP in the hopping mouse water deprivation response, with no effect of water deprivation on atrial NP mRNA receptors in the heart, but significant changes in the kidney (Heimeier et al 2002).…”

Vasopressin and oxytocin expression in hypothalamic supraoptic nucleus and plasma electrolytes changes in water-deprived male Meriones libycus

“…Plasma osmolality is often unaffected in many small desert mammals in experimental conditions when they are water-deprived, which indicates that they can compensate to remain in water balance and do not become dehydrated (see Degen 1997 ; Heimeier et al 2004 ; Heimeier and Donald 2006 ). Several processes have been described for maintaining body water content; including the production of metabolic water from body fat, the antidiuretic effect of AVP on urine concentration, and the extensive use of intracellular water (Horowitz and Adler 1983 ; Sicard 1987 ; Sicard 1992 ; Lacas et al 2000 ).…”