Heart and plasma atrial natriuretic peptide (ANP) in response to long-term endurance training in rats

Effect of exercise on gene expression of atrial natriuretic peptide receptor of kidney

To study the effect of exercise on gene expression of natriuretic peptide receptors (NPRs) in the kidney, with in situ hybridization and the computerized image analysis, we investigated the alterations of gene expression of NPRs on the animal model of exercise training of different intensity. We found that after exercise training of different intensity, renal NPR-A mRNA and NPR-C mRNA expression showed different changes, the expression of NPR-A mRNA upregulated and NPR-C mRNA downregulated in the kidney. With the increase exercise intensity, change in NPR-A mRNA expression was insignificant, but downregulation in NPR-C mRNA expression was more significant. The result suggested that the effect of exercise on renal NPRs mRNA expression was mainly on the modulation level of NPR-C mRNA, it could reduce the clearance rate of ANP, increase the level of ANP, and enhance the biological effect of ANP on the kidney and regulative action of kidney in exercise.

Cardiac natriuretic peptide response to water restriction in the hormonal adaptation of two semidesert rodents from West Africa (Steatomys caurinus, Taterillus gracilis)

Two African rodents, Taterillus gracilis and Steatomys caurinus, native to regions of alternate dry and wet seasons, were studied under laboratory conditions. These species differ in estivation behavior, one undergoing pseudoestivation and the other strong estivation. One group of animals of each species was provided with unlimited access to seed and vegetables rich in water, mimicking the food availability of the wet season (control group). A second group of animals of each species was subjected to water restriction for 8 days, mimicking the natural drought that occurs during the dry-hot season. The effects of water restriction on osmoregulation and body water content were assessed from hematocrit, and plasma and urinary osmolalities (PO, UO). Whether the natriuretic peptide system was modified by the osmoregulator adaptation to aridity of these semidesert rodents was examined from measurements of atrial natriuretic peptide (ANP) levels in plasma, atria, and ventricles, in parallel with morphological studies. In both species, UO was increased by water restriction. In water-deprived T. gracilis, ANP levels were about twice (right atria: 1.08 +/- 0.16 microg/mg protein vs control: 0.40 +/- 0.06 microg/mg protein) and plasma concentrations half (0.28 +/- 0.06 ng/ml vs control: 0.64 +/- 0.07 ng/ml) those in control animals. In S. caurinus these variables were not affected by water availability (right atria water restricted: 2. 20 +/- 0.15 microg/mg protein vs control: 2.86 +/- 0.37 microg/mg protein; plasma ANP water restricted: 0.80 +/- 0.12 ng/ml vs control: 0.90 +/- 0.16 ng/ml). Consistent with these quantitative results, immunohistochemical and ultrastructural observations showed an increase in immunostaining for both the N- and the C-terminal ANP and a larger number of granules in the atria of T. gracilis following water restriction, whereas there was no visible change in S. caurinus. Thus, water restriction induced a decrease in ANP secretion in T. gracilis, increasing cardiac storage alongside a reduced urine production. In contrast, in S. caurinus, the natriuretic system was not affected by an 8-day period of water restriction.

Presence of atrial natriuretic peptide in two desert rodents: comparison with rat

Atrial natriuretic peptide (ANP) was characterized and assayed in plasmas, hearts, and brains of two Algerian desert rodents, Psammomys obesus and Meriones libycus along with vasopressin, which was assayed in hypophyses and hypothalami. Using reverse-phase high-performance liquid chromatography and radioimmunoassay, we showed, in plasmas and hearts of both species of desert rats, the presence of peptides similar to rat N- and C-terminal ANP but in lower amounts than in Wistar rats. Conversely, C-terminal ANP was abundantly detected in hypophyses from Meriones libycus rats. As these peptides, through their diuretic and natriuretic activities, are involved in body fluid regulation and electrolyte balance, the reduction of ANP stores in both plasmas and hearts suggests that diuresis and natriuresis are lowered in both species of mammals adapted to arid environments. This could occur because of the vasopressin-mediated adaptation, but also in response to the low ANP involvement in hydro-osmotic regulations, even in Psammomys, which has a dietary salt loading. On the other hand, the higher C-terminal ANP contents in the hypophysis of Meriones than in Psammomys and Wistar rats remain to be understood.

Cellular adaptations of the myocardium to chronic exercise

The heart responds positively to programs of chronic dynamic exercise. Hallmark adaptations of the heart include a training bradycardia, increases in end-diastolic dimension and maximal stroke volume, and a general improvement in ventricular performance and contractile function. Of considerable clinical significance are the general observations that chronic exercise renders the myocardium less susceptible to the deleterious effects of acute ischemic episodes and can effectively prevent and/or reverse many of the cardiac functional deficits that are known to occur in settings of chronic hypertension, advanced age, and myocardial infarction. In the text that follows, information gathered over the last 25 to 30 years has been reviewed in an attempt to identify cellular myocardial adaptations, both known and hypothetical, that are responsible for the observed effects of chronic dynamic exercise on the function and morphology of the heart in both normal and selected pathophysiologic settings. Finally, a variety of unresolved issues regarding the ability of chronic exercise to elicit adaptive cardiocyte responses has been identified. In so doing, it is hoped that creative thought and future work in the area will be stimulated.