Marie D. Sauro

Prolactin stimulation of protein kinase C activity in rat aortic smooth muscle

Prolactin (PRL) activated protein kinase C (PKC) in a dose dependent manner in rat aortic smooth muscle. Aortic strips incubated with sub-nanomolar concentrations of ovine PRL for 25 min. at 37 degrees C showed a significant stimulation of PKC activity in both cytosolic and particulate fractions. This activation could be blocked using either anti-PRL antibodies or 1-(5- isoquinolinesulfonyl)-2-methylpiperazine (H-7), a PKC inhibitor. The results further support the role of PKC in the signal transduction pathway for PRL action and suggest that this activation may be involved in vascular smooth muscle function.

Prolactin and known modulators of rat splenocytes activate nuclear protein kinase C.

Prolactin (PRL) and other trophic factors rapidly activate a nuclear pool(s) of protein kinase C (nPKC) in purified splenocyte nuclei. The PRL also enhanced [2-3H]glycerol incorporation into nuclear mono- and triacylglycerol. An assay was devised which not only probed the ability of the hormone to activate protein kinase C (PKC) but also demonstrated the presence of nuclear substrates. Using this methodology, a biphasic concentration-response curve to PRL was observed. Heterologous species of PRL and various growth factors also activated nPKC. The PRL-induced nPKC stimulation was antagonized by various immunomodulators, G protein-coupling inhibitors, PKC inhibitors, a calmodulin inhibitor, and a peripheral benzodiazepine agonist and antagonist. A monoclonal antibody to PKC, anti-rat PRL antiserum and a monoclonal anti-rat PRL receptor antibody antagonized PRL-induced PKC-dependent nuclear phosphorylation, further implicating nPKC and a PRL receptor-mediated activation process. Nuclear PKC may be a major target for trophic regulation in response to both positive and negative growth signals.

Defective cyclic GMP accumulation in spontaneously hypertensive rat aorta in response to atrial natriuretic factor

Les mecanismes biochimiques responsables dune alteration de la reponse a la vasodilatation induite par le facteur ANF sont etudies chez le rat presentant une hypertension arterielle spontanee

Decreased sensitivity of aorta from hypertensive rats to vasorelaxation by tyrphostin

The role of protein tyrosine kinases (PTKs) in vascular smooth muscle (VSM) contraction was examined in spontaneously hypertensive rats (SHRs). Aorta from SHRs was hyperresponsive to PTK-mediated contraction relative to normotensive Wistar-Kyoto rats (WKYs). Aorta from SHR was also hyporesponsive to vasorelaxation by tyrphostin, a selective inhibitor of PTKs. Further, we found alterations in PTK activity in aorta from SHRs. PDGF stimulated PTK activity to a greater extent in the SHR. Tyrphostin inhibited PDGF-induced PTK stimulation in both strains, however, activity returned to basal levels in the WKY only. The results suggest that PTKs may be involved in VSM contraction and in the development of hypertension.

Gamma-interferon corrects aberrant protein kinase C levels and immunosuppression in the spontaneously hypertensive rat

The effects of gamma-interferon (gamma-IFN) on protein kinase C (PKC) levels and immunosuppression in the spontaneously hypertensive rat (SHR) were examined. First, an abnormal PKC distribution was found in spleen, thymus and aorta from SHRs relative to normotensive controls. Biweekly injections of rat recombinant gamma-IFN (1000 U/kg) restored basal or resting PKC levels to those found in normotensive Wistar-Kyoto (WKY) rats. We also examined the effects of in vivo gamma-IFN treatment on nuclear PKC (nPKC) activation in purified, isolated splenocyte nuclei. It was found that basal nPKC levels were higher in untreated SHRs than gamma-IFN SHRs or WKYs. Also, while nuclei from untreated SHRs were relatively unresponsive to various immunoreactive substances and PKC activators, gamma-IFN treatment significantly restored activity. Last, the proliferative response to mitogen challenge of isolated splenocytes from untreated SHRs, gamma-IFN-treated SHRs and WKYs was studied. Although gamma-IFN treatment did not restore the proliferative response to that of WKYs, the mitogen response was significantly enhanced by treatment with gamma-IFN. The data show that gamma-IFN acts to restore normal immune function and corrects aberrant PKC levels and adds to the growing body of knowledge suggesting a role for immune dysfunction in the etiology of hypertension.

Decreased sensitivity of spontaneously hypertensive rat aortic smooth muscle to vasorelaxation by atriopeptin III

The effects of a synthetic form of Atrial Natriuretic Factor (ANF) on spontaneously hypertensive rat aortic smooth muscle were investigated using either an alpha-adrenoceptive agonist (phenylephrine) or an agent which partially depolarized the plasma membrane (20mM KCl) as a contractile agent. The relaxant response was studied under conditions resembling normal physiological calcium ion levels (1.5mM) as well as over a range of calcium ion concentrations (0.1-2.5mM). The results demonstrate a hyporesponsiveness of hypertensive aorta to vasorelaxation induced by synthetic ANF, which is more apparent when the tissue is contracted with KCl. The results also suggest that ANF, which has been shown previously to inhibit intracellular and receptor operated calcium channel mobilization only, may additionally work through a mechanism which is related to the voltage induced calcium flux across the membrane, which also is inhibited less in hypertensive smooth muscle.

Prolactin induces growth-related gene expression in rat aortic smooth muscle in vivo☆

We examined the effects of in vivo administration of prolactin on growth-related gene expression in aorta. Optimal mRNA expression for both the proto-oncogene, c-myc and ornithine decarboxylase occurred at 22 mg/kg prolactin. For c-myc, this was seen as early as 15 min. Prolactin-induced ornithine decarboxylase mRNA expression began at 1 h. The results confirm work showing induction of these genes by prolactin in tissues where it is mitogenic and supports a role for prolactin in the trophic response of vascular smooth muscle.

Atrial peptides inhibit protein kinase C-mediated contraction in rat aorta

The effects of atriopeptin III on phorbol ester-induced contraction were examined in aorta from Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Precontracted SHR aorta was less responsive than WKY aorta to atriopeptin III-induced relaxation. Additionally, SHR aorta had significantly greater basal and phorbol ester-stimulated protein kinase C (PKC) activity than WKY aorta. The altered PKC response as well as hyporesponsiveness to atriopeptin III in SHR aorta may contribute to an altered vascular response and to the pathogenesis of hypertension.

Prolactin Receptors in the Nervous and Immune Systems

Prolactin, an anterior pituitary hormone with a multitude of roles and sites of action, is produced in lactrotrophs and is one of a family of four to six somatomammotropic hormones. A great diversity of functions has been ascribed to prolactin in many different species. Of particular recent importance has been the emergence of substantial evidence indicating that prolactin acts as a modulator of the immune response in mammals (1,2; see also Carr, this volume). Furthermore, prolactin has been identified in various areas of the brain and appears to play a role in neural function. Thus, prolactin appears to function as an immunomodulator and may in fact influence some events within the nervous system of mammals. It is very likely that bidirectional communication exists between the nervous and immune systems (3), and prolactin seems to play an important role in this process.

Adenosine activation of a nuclear pool of protein kinase C in rat splenocytes

The stimulatory effects of adenosine analogues on a nuclear pool of protein kinase C (PKC) were examined using isolated rat splenocyte nuclei. Nuclear receptors met pharmacological criteria of A1 adenosine receptors including a potency profile in which cyclopentyladenosine (CPA), a selective A1 agonist, was more potent than 2-phenylaminoadenosine (2PAA), a selective A2 agonist. The selective A1 receptor agonist N6-1-(phenyl-2R-propyl) adenosine (R-PIA) activated PKC whereas the S diastereomer did not. The adenosine-induced PKC response could be attenuated using a monoclonal antibody to PKC, an A1 receptor antagonist, three known PKC inhibitors and pertussis toxin (PTX). The results suggest that adenosine may exert immunomodulatory effects through the activation of nuclear PKC.