A synthetic oligonucleotide probe encoding for atrial natriuretic peptide detects specific mRNA transcripts in rat heart but not brain using in situ hybridization histochemistry

In situ hybridization histochemical techniques were used in an attempt to demonstrate atrial natriuretic peptide (ANP) messenger RNA (mRNA) in the rat brain. A synthetic oligonucleotide derived from previously reported ANF cDNA sequence was used as a probe. Northern blot analysis of total RNA isolated from rat heart demonstrated that the oligonucleotide recognized a single species of RNA (0.9 kb), a size consistent with previous reports. Rat heart sections revealed dense accumulations of ANF mRNA in the cardiac atria and lesser densities in the ventricles. Rat brain sections hybridized with the same oligonucleotide did not label ANF mRNA accumulations in any neuronal cell bodies. A possible explanation for this latter observation is either sparsely distributed expressing neurons or low expression and high turnover of ANF mRNA in brain.     

Atrial natriuretic peptide in the central nervous system of the rat

1. Studies of the presence of atrial natriuretic peptide immunoreactivity and receptor binding sites in the central nervous system have revealed unusual sites of interest. 2. As a result, numerous studies have appeared that indicate that brain atrial natriuretic peptide is implicated in the regulation of blood pressure, fluid and sodium balance, cerebral blood flow, brain microcirculation, blood-brain barrier function, and cerebrospinal fluid production. 3. Alteration of the atrial natriuretic peptide system in the brain could have important implications in hypertensive disease and disorders of water balance in the central nervous system.     

Effect of calcitonin gene-related peptide on the neuroeffector mechanism of sympathetic nerve terminals in rat vas deferens

In order to evaluate the mode of action of calcitonin gene-related peptide (CGRP) on the neuroeffector mechanism of peripheral sympathetic nerve fibers, the effects of CGRP were tested on the electrical stimulated and the non-stimulated preparations of the isolated rat vas deferens. The contractile responses, which were mediated predominantly by activation of postganglionic noradrenergic nerve fibers, were dose-dependently inhibited by CGRP in concentrations ranging from 0.1 to 10 nM. The inhibitory response produced by CGRP in high concentrations (greater than 2 nM) usually returned to the control level at 20-30 min and were rarely tachyphylactic. The inhibitory action of CGRP was not modified by pretreatment with 10(-7) M propranolol or 10(-7) M atropine. Contractions produced by exogenous norepinephrine (NE) and 5-hydroxytryptamine (5-HT) in unstimulated preparations were not affected by pretreatment with CGRP in a low concentration (less than 2 nM). On the other hand, the contractions were slightly reduced 1 min after pretreatment with CGRP in high concentrations (greater than 5 nM), which recovered in 15 min after constant flow washout. High concentrations of CGRP also caused a concentration-dependent relaxation on the precontracted preparations produced by high potassium (60 mM K+) solution. These results suggest that CGRP in high concentrations (greater than 5 nM) may have a non-specific inhibitory action on the postsynaptic plasma membrane of the smooth muscle cell and a postulated CGRP receptor exists presynaptically in the rat vas deferens and that CGRP may inhibit the release of NE during adrenergic nerve stimulation.     

Iron Deficiency Alters Discrete Proteins in Rat Caudate Nucleus and Nucleus Accumbens

Young rats (21 days old) made nutritionally iron deficient, by feeding them a semisynthetic diet containing skimmed milk for 5 weeks, had significantly lowered hemoglobin levels (5.2 +/- 4 g/100 ml). The nonheme iron content in caudate nucleus was decreased by 47%. The behavioral response of iron-deficient rats to apomorphine (2 mg/kg) and the density of 3,4-dihydroxyphenylethylamine (dopamine) D2 receptors, as measured by [3H]spiperone binding in caudate nucleus, were significantly reduced by 70 and 53%, respectively. The possibility that nutritional iron deficiency may affect protein content in brain was investigated by measuring the apparent concentration of proteins in caudate nucleus and nucleus accumbens from iron-deficient and control animals using two-dimensional gel electrophoresis. The data indicate that iron deficiency can affect content in these two brain regions. Significant changes in the content of 10 proteins were noted in the caudate nucleus and nucleus accumbens in iron-deficient rats. The albumin level was significantly increased in both regions studied, whereas the neuron-specific enolase level was increased in the nucleus accumbens and the glial fibrillary acidic protein level was reduced in the caudate nucleus. The significance of these protein content changes, as well as a reduction in content of a 94-kilodalton protein (a molecular size similar to that of the D2 dopamine receptor), remains to be established.     

Propranolol and methylatropine antagonize the cardiovascular effects produced by microinjection of the TRH analog MK-771 into the preoptic suprachiasmatic nucleus

Thyrotropin-releasing hormone (TRH) has been shown to increase heart rate as well as blood pressure when administered into rat brain. The present study investigated the mechanism by which the TRH analog MK-771 produces these effects when injected into the preoptic suprachiasmatic nucleus (POSC). MK-771, at a dose of 125 pmol (50 ng), produced significant increases in both heart rate and blood pressure. These effects occurred within 5 minutes of microinjection and lasted approximately 20-30 minutes. Pretreatment with either the beta-adrenergic antagonist propranolol or the muscarinic antagonist methylatropine, administered into the POSC, significantly altered the response produced by MK-771. Propranolol, at a dose of 7 nmol, and methylatropine at a dose of 0.5 nmol, significantly inhibited the tachycardia produced by MK-771. In addition, methylatropine, at a dose of 0.5 nmol, significantly reduced the increase in diastolic pressure produced by the TRH agonist. These results are consistent with the idea that TRH agonists, when administered centrally, produce cardiovascular alterations through the autonomic nervous system.