Evidence for attenuation of myo-inositol uptake, phosphoinositide turnover and inositol phosphate production in aortic vasculature of rats during pregnancy

The renal circulation in normal pregnancy and preeclampsia: is there a place for relaxin?

During the first trimester of human pregnancy, the maternal systemic circulation undergoes remarkable vasodilation. The kidneys participate in this vasodilatory response resulting in marked increases in renal plasma flow (RPF) and glomerular filtration rate (GFR). Comparable circulatory adaptations are observed in conscious gravid rats. Administration of the corpus luteal hormone relaxin (RLN) to nonpregnant rats and humans elicits vasodilatory changes like those of pregnancy. Systemic and renal vasodilation are compromised in midterm pregnant rats by neutralization or elimination of circulating RLN and in women conceiving with donor eggs who lack a corpus luteum and circulating RLN. Although RLN exerts both rapid (minutes) and sustained (hours to days) vasodilatory actions through different molecular mechanisms, a final common pathway is endothelial nitric oxide. In preeclampsia (PE), maternal systemic and renal vasoconstriction leads to hypertension and modest reduction in GFR exceeding that of RPF. Elevated level of circulating soluble vascular endothelial growth factor receptor-1 arising from the placenta is implicated in the hypertension and disruption of glomerular fenestrae and barrier function, the former causing reduced Kf and the latter proteinuria. Additional pathogenic factors are discussed. Last, potential clinical ramifications include RLN replacement in women conceiving with donor eggs and its therapeutic use in PE. Another goal has been to apply knowledge gained from investigating circulatory adaptations in pregnancy toward identifying and developing novel therapeutic strategies for renal and cardiovascular disease in the nonpregnant population. So far, one candidate to emerge is RLN and its potential therapeutic use in heart failure.

Receptor-induced dilatation in the systemic and intrarenal adaptation to pregnancy in rats

Normal pregnancy is associated with systemic and intrarenal vasodilatation resulting in an increased glomerular filtration rate. This adaptive response occurs in spite of elevated circulating levels of angiotensin II (Ang II). In the present study, we evaluated the potential mechanisms responsible for this adaptation. The reactivity of the mesangial cells (MCs) cultured from 14-day-pregnant rats to Ang II was measured through changes in the intracellular calcium concentration ([Cai]). The expression levels of inducible nitric oxide synthase (iNOS), the Ang II-induced vasodilatation receptor AT2, and the relaxin (LGR7) receptor were evaluated in cultured MCs and in the aorta, renal artery and kidney cortex by real time-PCR. The intrarenal distribution of LGR7 was further analyzed by immunohistochemistry. The MCs displayed a relative insensitivity to Ang II, which was paralleled by an impressive increase in the expression level of iNOS, AT2 and LGR7. These results suggest that the MCs also adapt to the pregnancy, thereby contributing to the maintenance of the glomerular surface area even in the presence of high levels of Ang II. The mRNA expression levels of AT2 and LGR7 also increased in the aorta, renal artery and kidney of the pregnant animals, whereas the expression of the AT1 did not significantly change. This further suggests a role of these vasodilatation-induced receptors in the systemic and intrarenal adaptation during pregnancy. LGR7 was localized in the glomeruli and on the apical membrane of the tubular cells, with stronger labeling in the kidneys of pregnant rats. These results suggest a role of iNOS, AT2, and LGR7 in the systemic vasodilatation and intrarenal adaptation to pregnancy and also suggest a pivotal role for relaxin in the tubular function during gestation.

Glucose-Dependent Enhancement of Spontaneous Phasic Contraction Is Suppressed in Diabetic Mouse Portal Vein: Association with Diacylglycerol-Protein Kinase C Pathway

We investigated portal vein (PV) contractility in diabetes using a mouse model (ob/ob mouse) of spontaneous noninsulin-dependent diabetic mellitus. Spontaneous phasic contraction in control mice (C57Bl) was increased in the presence of the thromboxane A(2) analog 9,11-dideoxy-11alpha, 9alpha-epoxymethanoprostaglandin F(2)alpha (U46619) in a time- and concentration-dependent manner. This response was enhanced under high glucose conditions (22.2 mM). Diacylglycerol (DG) was synthesized from glucose and was not affected by phospholipase C (PLC) inhibition under resting conditions in normal glucose. Inhibition of DG-induced PKC activation with 12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo-(2,3-alpha)pyrrolo(3,4-c)-carbazole (Gö6976), a calcium-dependent protein kinase C (PKC) inhibitor, was only observed under normal glucose conditions. High glucose levels enhanced PLC-independent DG formation followed by an induction of total phosphatidylinositol turnover via calcium-independent PKC activation in C57Bl mice. In ob/ob mice, the high glucose-induced enhancement of PV contraction in response to U46619 was suppressed. These findings suggest that these differences are associated with long-term exposure of tissue to a hyperglycemic state. Under high glucose conditions, DG derived from glucose fell below 50% in C57Bl mice. Moreover, the DG-related calcium-independent PKC was desensitized in ob/ob mice. These results suggest that suppression of the glucose-induced enhancement of PV contraction involves both a decrease in glucose-derived DG formation and reduction of the glucose sensitivity of DG-related PKC.

High-glucose enhances a thromboxane A2-induced aortic contraction mediated by an alteration of phosphatidylinositol turnover

The effect of the thromboxane A(2) analogue U46619 (9,11-dideoxy-11alpha,9alpha-epoxymethanoprostaglandin F(2)(alpha)) on sustained contraction in the mouse aorta was investigated. U46619 induced concentration-dependent (1 - 100 nM) increases in contraction. These contractile responses were enhanced significantly under high-glucose-physiological salt solution (HG-PSS) (2-fold greater than normal-PSS) conditions. This hyperactivation may be associated with aortic dysfunction in diabetes. However, the mechanisms remain unclear. HG-PSS enhanced U46619-induced accumulation of endogenous diacylglycerol (DG). Phospholipase C inhibitor (U73122) suppressed DG accumulation under normal conditions; however, suppression was not observed under high-glucose conditions. The HG-PSS-induced enhancement of contraction was inhibited by protein kinase C (PKC) inhibitor (calphostin C). This result indicated that accumulated DG might increase PKC activity, which then stimulates DG kinase activation as a feedback mechanism. DG kinase inhibition also suppressed HG-PSS-induced enhancement of contraction. Increased myo-inositol incorporation was detected under high-glucose conditions, indicating an acceleration of phosphatidylinositol (PI)-turnover. Moreover, rho kinase inhibitor (Y27632) suppressed U46619-induced contraction exclusively in normal-PSS. These findings indicated that HG-PSS treatment increases DG synthesis derived from incorporated glucose, PKC and DG kinase activation, and enhances the U46619-induced contraction via acceleration of PI-turnover. This series of responses may be involved in the dysfunction of aorta under high-glucose conditions occurring in association with diabetes.

Dysfunction of aorta involves different patterns of intracellular signaling pathways in diabetic rats

Rat models of insulin-dependent (streptozotocin-induced) and independent (Otsuka Long-Evans Tokushima Fatty (OLETF)) diabetes had sustained and transient increases in blood glucose levels. Over-contraction due to norepinephrine was seen exclusively in streptozotocin rat aorta. Contraction was enhanced under high-glucose conditions in OLETF rats. In order to understand the association between these patterns of changes, total diacylglycerol was measured as a key element of phosphatidylinositol-turnover due to the conversion of some incorporated glucose into diacylglycerol. Streptozotocin rats had enhanced basal diacylglycerol. Both diacylglycerol kinase (metabolic enzyme of diacylglycerol) and total phosphatidylinositol turnover activities also increased on norepinephrine stimulation, independent of extracellular glucose level. On the other hand, diacylglycerol, diacylglycerol kinase and phosphatidylinositol turnover in OLETF rats increased under high glucose conditions in the absence of norepinephrine treatment. These results indicated that diacylglycerol and diacylglycerol kinase-mediated phosphatidylinositol turnover acceleration was influenced by an increase in glucose levels in OLETF rats or by receptor-mediated signals in streptozotocin rats including glucose desensitization based on submaximal incorporation. We suggest that the alteration of vascular dysfunction is induced by different factors in each type of diabetes.

Enhancement effect under high-glucose conditions on U46619-induced spontaneous phasic contraction in mouse portal vein

The effect of the thromboxane A(2) analog 9,11-dideoxy-11alpha, 9alpha-epoxymethanoprostaglandin F(2alpha) (U46619) on spontaneous phasic contractions in the mouse portal vein was studied. U46619 induced concentration-dependent (1-100 nM) increases in amplitude, frequency, and contractile period (ON-time) of the contraction. Both amplitude and ON-time were enhanced significantly under high-glucose (HG; 4-fold greater than normal) conditions. This hyperactivation may be associated with portal vein dysfunction in diabetes. However, the mechanisms remain unclear. HG enhanced the U46619-induced accumulation of endogenous diacylglycerol (DG). Phospholipase C inhibition suppressed accumulation under normal conditions; however, this suppression was not observed under HG conditions. The HG-induced enhancement of U46619-induced contraction was inhibited by protein kinase C (PKC) inhibition. This finding indicated that accumulated DG might increase PKC activity. Activated PKC stimulated DG kinase activation as a feedback mechanism. DG kinase inhibition also suppressed the HG-induced enhancement of contraction. Increased myo-inositol incorporation was detected under HG conditions, indicating an acceleration of phosphatidylinositol (PI) turnover. This acceleration was inhibited by PKC and DG kinase inhibitors. These findings indicated that HG treatments increased DG synthesis derived from incorporated glucose, PKC, and DG kinase activation. These responses induce hyperactivation of the amplitude and contractile period of contraction mediated by acceleration of PI turnover. This series of responses may be involved in the dysfunction of the portal vein under the HG conditions occurring with diabetes.

Vascular mechanisms of increased arterial pressure in preeclampsia: lessons from animal models

Normal pregnancy is associated with reductions in total vascular resistance and arterial pressure possibly due to enhanced endothelium-dependent vascular relaxation and decreased vascular reactivity to vasoconstrictor agonists. These beneficial hemodynamic and vascular changes do not occur in women who develop preeclampsia; instead, severe increases in vascular resistance and arterial pressure are observed. Although preeclampsia represents a major cause of maternal and fetal morbidity and mortality, the vascular and cellular mechanisms underlying this disorder have not been clearly identified. Studies in hypertensive pregnant women and experimental animal models suggested that reduction in uteroplacental perfusion pressure and the ensuing placental ischemia/hypoxia during late pregnancy may trigger the release of placental factors that initiate a cascade of cellular and molecular events leading to endothelial and vascular smooth muscle cell dysfunction and thereby increased vascular resistance and arterial pressure. The reduction in uterine perfusion pressure and the ensuing placental ischemia are possibly caused by inadequate cytotrophoblast invasion of the uterine spiral arteries. Placental ischemia may promote the release of a variety of biologically active factors, including cytokines such as tumor necrosis factor-alpha and reactive oxygen species. Threshold increases in the plasma levels of placental factors may lead to endothelial cell dysfunction, alterations in the release of vasodilator substances such as nitric oxide (NO), prostacyclin (PGI(2)), and endothelium-derived hyperpolarizing factor, and thereby reductions of the NO-cGMP, PGI(2)-cAMP, and hyperpolarizing factor vascular relaxation pathways. The placental factors may also increase the release of or the vascular reactivity to endothelium-derived contracting factors such as endothelin, thromboxane, and ANG II. These contracting factors could increase intracellular Ca(2+) concentrations ([Ca(2+)](i)) and stimulate Ca(2+)-dependent contraction pathways in vascular smooth muscle. The contracting factors could also increase the activity of vascular protein kinases such as protein kinase C, leading to increased myofilament force sensitivity to [Ca(2+)](i) and enhancement of smooth muscle contraction. The decreased endothelium-dependent mechanisms of vascular relaxation and the enhanced mechanisms of vascular smooth muscle contraction represent plausible causes of the increased vascular resistance and arterial pressure associated with preeclampsia.

Hyper-reactivity of diacylglycerol kinase is involved in the dysfunction of aortic smooth muscle contractility in streptozotocin-induced diabetic rats

1. Dysfunction of vascular contraction in diabetes has been reported; however, the mechanisms are poorly understood. In this study, calcium sensitization involving increases in contraction in streptozotocin-induced diabetic rat aorta was detected. We hypothesize that an alteration in the intracellular signalling system plays a role in the dysfunction of vascular contractility in diabetes. Therefore, diacylglycerol (DG) kinase as a key enzyme of phosphatidylinositol (PI) turnover was investigated. 2. Treatment with norepinephrine (NE) caused time- and dose-dependent activation of DG kinase in control rats. This activation required simultaneous increases in intracellular calcium concentration ([Ca2+]i) and protein kinase C (PKC) activation. I3. n diabetic rats, hyper-reactivity of DG kinase involving inactivation in the resting state and over-activation in NE stimulation was observed. During hyper-reactivity, [Ca2+]i dependency of DG kinase was enhanced. Treatment with 50 mM KCl induced significant escalation in activity; moreover, basal activation of PKC was detected only in diabetes. These results suggested that PKC had been activated in the resting state. In contrast, these conditions were insufficient for DG kinase activation due to the absence of [Ca2+]i elevation. 4. During NE-stimulation, PKC activation was maintained and [Ca2+]i increased. Therefore, DG kinase was activated and an elevation in calcium dependency enhanced this activation. 5. The present study suggested that DG kinase hyper-reactivity in diabetes involved both an increase in [Ca2+]i and basal activation of PKC. This phenomenon may be associated with increased vascular contraction in diabetes mediated by acceleration of PI-turnover.

Enhanced vascular effects of the Ca(2+) channel agonist Bay K 8644 in pregnant rabbits

Hemodynamic studies were performed to determine if blunting of vascular pressor responsiveness to vasoconstrictors during pregnancy may be due to impaired L-type voltage-dependent calcium channels (L-VDCC). Bay K 8644 (BAY), an L-VDCC agonist, was infused in pregnant and nonpregnant anesthetized rabbits (10, 20, 40, and 60 microg/kg) and pregnant and nonpregnant conscious, chronically instrumented (conscious) rabbits (10, 25, and 50 microg/kg). BAY infusions resulted in greater elevation of mean arterial pressure in both anesthetized pregnant (n = 6) vs. nonpregnant (n = 6) (P < 0.05) and conscious pregnant (n = 10) vs. nonpregnant (n = 10) rabbits (P < 0.05). Fractional increase over baseline of total peripheral resistance index was greater in pregnant (36 +/- 5 to 78 +/- 14%) vs. nonpregnant rabbits (14 +/- 4 to 52 +/- 6%) (P < 0.02). Cardiac output index did not differ. There was a single high-affinity L-VDCC antagonist aortic binding site with similar number and affinity in pregnant (n = 7) and nonpregnant (n = 7) rabbits. In conclusion, stimulation of L-VDCC induces greater pressor responses in pregnant rabbits with heightened peripheral vasoconstriction. This does not appear to be due to a change in L-VDCC receptor parameters.

Responses of isolated perfused uterine vascular beds of nonpregnant and pregnant rats to endogenous and exogenous nitric oxide

The responses to endothelial vasodilators and exogenous nitric oxide (NO) were characterized in intact isolated uterine vascular beds of nonpregnant, midpregnant and late-pregnant rats perfused with Kreb's buffer (37 degrees C, 5% CO(2) in air, pH approximately 7.4) containing 2% dextran and indomethacin. Phenylephrine increased perfusion pressure in the vascular beds equally in all three groups. In the presence of phenylephrine, N(omega)-nitro-L-arginine methyl ester (L-NAME) significantly augmented perfusion pressure in the order: nonpregnant<midpregnant<late-pregnant uterine vascular bed. Acetylcholine and bradykinin-induced attenuation of perfusion pressure did not depend on gestational age. The decrease in perfusion pressure induced by acetylcholine was nonsignificantly attenuated by L-NAME in vascular beds from pregnant rats. The attenuation induced by bradykinin reached significant level in the vascular beds from midpregnant rats. The diethylamine (DEA)/NO-induced decrease in perfusion pressure was not influenced by L-NAME in any group. These data demonstrate the augmentation of basal release of NO associated with progression of pregnancy, while the responses to endothelial vasodilators do not depend on gestational age and are not abolished by inhibition of NO synthase, suggesting involvement of nonprostanoid non-NO factor in the control of uterine circulation.

Pregnancy is not associated with altered morphology of the femoral artery

While pregnancy is associated with adjustments in cardiovascular function, the morphology of the vascular system during pregnancy has been generally viewed as being very stable. However, recently we have demonstrated that pregnancy remodels the aorta and the carotid artery. In the present study, we assessed the morphological characteristics of the guinea-pig femoral artery during different stages of pregnancy using light and electron microscopy. There were no significant differences between external and internal diameters, wall thickness, total cross-sectional area and cross-sectional areas of lumen, intima, media, and adventitia of femoral arteries from non-pregnant and early-, mid- and late-pregnant guinea-pigs (n = 8-10). In previous studies, we have shown that the morphology of vascular smooth muscle and endothelial cells in the aorta and the carotid artery may be altered by pregnancy. Therefore, to test this possibility we measured diameters as well as cross-sectional areas of femoral arterial muscle and endothelial cells using electron microscopy. These parameters, at the electron microscopy level, were also not significantly changed by pregnancy (n = 8-10). It is concluded that the morphology of the guinea-pig femoral artery is not altered during pregnancy. In this regard, this study demonstrated that pregnancy-induced vascular remodelling varies between blood vessels that undergo the same functional alterations. Therefore, this may suggest that pregnancy-induced changes in blood flow through different vascular beds are not the most important factor involved in vascular remodelling observed during pregnancy. Rather, it is possible that haemodynamic-independent factors regulate pregnancy-mediated structural changes of the vascular wall.

Endothelial nitric oxide release in isolated perfused ovine uterine arteries: effect of pregnancy

The present study was designed to determine the release of endothelial nitric oxide, measured as combined nitric oxide, nitrite and nitrate (NOx), in isolated perfused uterine arteries obtained from nonpregnant and pregnant sheep. Noradrenaline produced concentration-dependent increases in perfusion pressure in both nonpregnant and pregnant uterine arteries with pD2 values of 5.1+/-0.07 and 4.6+/-0.04, respectively. The maximum responses were 300.8+/-8.8 mmHg for nonpregnant arteries and 86.9+/-1.3 mmHg for pregnant ones. N(G)-nitro-L-arginine increased noradrenaline-mediated maximum response in the pregnant (86.9+/-1.3 to 144.6+/-5.1 mmHg), but not in the nonpregnant, uterine arteries. The basal level of NOx was significantly higher in pregnant than in nonpregnant uterine arteries (346.1+/-63.2 vs. 86.0+/-20.6 pmol/ml). The calcium ionophore A23187 and adenosine triphosphate produced concentration-dependent increases in NOx release in both nonpregnant and pregnant arteries. Compared to the nonpregnant tissue, the agonist-induced increase in NOx release was significantly enhanced in the pregnant uterine artery. In accordance, endothelial NO synthase protein expression in pregnant uterine artery was 197% of that in nonpregnant artery. These data indicate that in the uterine artery, pregnancy increases both basal and agonist-induced release of endothelial nitric oxide, which is likely to play a key role in attenuated vascular reactivity of the uterine artery to vasoconstrictors during the course of pregnancy.

Hemodynamic and hormonal responses to hemorrhage in conscious rabbits at mid- and late gestation

This study tests the hypothesis that conscious rabbits late in pregnancy (P), but not at midgestation (MP), are less able to maintain arterial pressure during hemorrhage. Blood volume (BV) was elevated (P < 0.05) by an average of 13 +/- 4 (MP) and 35 +/- 3% (P). Rabbits were bled in both the nonpregnant (NP) and P state at 2% of the initial BV per minute. The hemorrhage was stopped after arterial pressure decreased. In NP rabbits, arterial pressure was well maintained near control pressures of 70 +/- 2 mmHg until 38 +/- 2% of the initial BV was removed and then rapidly fell to reach a nadir at 35 +/- 2 mmHg. In contrast, in P rabbits, basal arterial pressure was lower (61 +/- 2 mmHg; P < 0.05) and gradually decreased to below control after <25% of the initial BV was removed. Moreover, the rapid hypotensive phase was triggered with a lower percent BV removal (33 +/- 2%; P < 0.05). Basal heart rate was higher during P (149 +/- 5 vs. 189 +/- 9 beats/min; P < 0.05), and reflex increases were delayed. The slope of the relationship between arterial pressure and vasopressin was not modified during P, although the line was shifted to a lower pressure (P < 0.05). Larger increases in plasma renin activity and ANG II concentration were produced during hemorrhage in P rabbits. In contrast, no differences in the changes in arterial pressure, heart rate, and vasopressin were found between NP and MP rabbits during hemorrhage, although increases in renin and ANG II were greater at MP (P < 0.05). In summary, although P conscious rabbits are less able to maintain blood pressure during hemorrhage, this change is not evident at MP. These data suggest that the factors that mediate the P-induced alterations in arterial pressure regulation are not operative until late in gestation.

Acute blockade of nitric oxide synthase inhibits renal vasodilation and hyperfiltration during pregnancy in chronically instrumented conscious rats

Because the kidneys are vasodilated and the endogenous production of nitric oxide is increased in gravid rats, we tested whether nitric oxide mediates the renal vasodilatory response to pregnancy. Chronically instrumented, conscious rats of gestational days 12-14 were studied concurrently with age-matched virgin control animals. GFR and effective renal plasma flow (ERPF) were determined by the renal clearances of inulin and para-aminohippurate before and during acute infusion of N omega-nitro-L-arginine methyl ester (NAME; 2, 20, and 50 micrograms/min) or NG-monomethyl-L-arginine (100 micrograms/min). Baseline GFR and ERPF were significantly increased, and effective renal vascular resistance was decreased by 30-40% in gravid rats compared with virgin controls. During infusion of all three dosages of NAME and NG-monomethyl-L-arginine, effective renal vascular resistance, GFR, and ERPF were equalized in the pregnant and virgin rats (the only exception being GFR during the 20 micrograms/min NAME infusion). When compared with virgin rats, the gravid animals were more responsive to nitric oxide synthase inhibition, showing a significantly greater decline in GFR and ERPF and rise in effective renal vascular resistance at each timepoint during the infusion of inhibitor. To exclude the possibility that nonspecific renal vasoconstriction per se led to equalization of renal function in the two groups of rats, we investigated angiotensin II. In contrast to the results observed with nitric oxide synthase inhibitors, pregnant rats were less responsive to the renal vasoconstrictory effects of angiotensin II, such that the baseline differences in renal parameters measured before infusion of the hormone were increased during the infusion. To determine whether nitric oxide synthase was inhibited to a similar extent in gravid and virgin rats, aortic and renal cortical cGMP content was assayed ex vivo at the end of inhibitor infusion. The lower 2-micrograms/min dose of NAME consistently reduced cGMP content of these tissues to comparable levels in the two groups of rats. In conclusion, we suggest that nitric oxide mediates reduced renal vascular resistance and hyperfiltration during pregnancy in conscious rats.

Effects of pregnancy and progesterone metabolites on regulation of sympathetic outflow

1. Pregnancy is characterized by a 40% increase in blood volume and cardiac output, a decrease in arterial blood pressure and thus a substantial decrease in total peripheral resistance. The aims of the experiments described in this manuscript were: (i) to determine if pregnancy resulted in alterations in baroreflex control of sympathetic outflow; and (ii) to evaluate possible mechanisms for pregnancy-induced changes in control of sympathetic outflow. 2. Arterial baroreflex control of efferent renal sympathetic nerve activity was examined in female pregnant and non-pregnant normotensive Sprague-Dawley and Wistar-Kyoto rats. In both rat strains, pregnancy was associated with a decrease in baseline arterial pressure, a shift in the baroreflex function curve to a lower operating pressure range and an attenuated ability to reflexly increase sympathetic outflow above baseline levels during a hypotensive challenge. Pregnant Sprague-Dawley rats retained their ability to respond to a hypertensive challenge, whereas pregnant Wistar-Kyoto rats exhibited a decreased sensitivity to hypertensive as well as hypotensive challenges. 3. The inhibitory amino acid transmitter, GABA, mediates baroreflex sympatho-inhibition within the rostral ventral lateral medulla (RVLM) of the brainstem. Since 3 alpha-OH dihydroprogesterone (3 alpha-OH-DHP), a major metabolite of progesterone, is elevated in pregnancy and has been reported to potentiate central nervous system GABAA inhibitory responses, experiments were performed to determine if effects of this metabolite of progesterone could contribute to the pregnancy associated changes in control of sympathetic outflow.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitric oxide biosynthesis during pregnancy: implications for circulatory changes

1. The biosynthesis of NO and its second messenger, cGMP, increases from pre-pregnant levels during rat gestation. An increase in plasma level and urinary excretion of cGMP is also evident during human pregnancy. However, the relative contribution of the maternal vasculature and other tissues to increased NO and cGMP biosynthesis during gestation is uncertain. Consensus is lacking about the contribution of NO to reduced maternal vascular tone and reactivity during gestation in various organ beds; clearly, further investigation is still needed. That NO may also regulate vascular smooth muscle behaviour during pregnancy by altering membrane potential is another intriguing possibility. 2. The syncytiotrophoblast of the human placenta expresses significant NO synthase activity, and along with the fetoplacental endothelium undoubtedly contributes to NO production during pregnancy. 3. Finally, it should be emphasized that vascular studies in gravid animal models need to be extended to pregnant women.

Altered protein kinase C regulation of phosphoinositide-coupled receptors in deoxycorticosterone acetate-salt hypertensive rats

This study examined the contribution of phosphatidylinositol metabolism and the efficacy of protein kinase C-mediated desensitization in the exaggerated alpha 1b-adrenergic receptor-mediated inositol phosphate response in the aorta of the deoxycorticosterone acetate (DOCA)-salt rat model of hypertension. The basal accumulation of inositol phosphates and the basal incorporation of [3H]myo-inositol in the phosphatidylinositol lipid pool were significantly higher in the aorta of these hypertensive rats. A positive correlation (r = .88, P < .01) was demonstrated between basal inositol phosphate levels and the [3H]myo-inositol-labeled phosphatidylinositol lipid pool. In hypertensive rats, alpha 1b-adrenergic receptor-mediated inositol phosphate production in response to phenylephrine was significantly higher compared with normotensive rats. Despite the normalization of phenylephrine-mediated inositol phosphate production to the [3H]myo-inositol-labeled phosphatidylinositol lipid pool, the alpha 1b-adrenergic response remained significantly higher in the hypertensive rats. Phorbol ester activation of protein kinase C attenuated to a lesser extent phenylephrine-mediated inositol phosphate production (40%) in the aorta of hypertensive rats compared with the 80% attenuation observed in the aorta of normotensive rats. This desensitization was inhibited in both groups by the protein kinase C inhibitor staurosporine. The blunted desensitization of the alpha 1b-adrenergic receptor by protein kinase C activation was not associated with a decrease in protein kinase C activity in the hypertensive rats, because aortic strips from these animals were more responsive to phorbol ester activation than aortic strips from normotensive animals.(ABSTRACT TRUNCATED AT 250 WORDS)