The rostral ventrolateral medulla (RVLM) contains neurons involved in tonic and reflex control of arterial pressure. We describe the effects of gamma-aminobutyric acid (GABA) and anesthetics injected into the RVLM of conscious and urethane (1.2 g/kg, iv) anesthetized Wistar rats (300-350 g). In conscious rats, bilateral microinjection of GABA (50 nmol/200 nl) induced a small but significant decrease in blood pressure (from 130 ± 3.6 to 110 ± 5.6 mmHg, N = 7). A similar response was observed with sodium pentobarbital microinjection (24 nmol/200 nl). However, in the same animals, the fall in blood pressure induced by GABA (from 121 ± 8.9 to 76 ± 8.8 mmHg, N = 7) or pentobarbital (from 118 ± 4.5 to 57 ± 11.3 mmHg, N = 6) was significantly increased after urethane anesthesia. In contrast, there was no difference between conscious (from 117 ± 4.1 to 92 ± 5.9 mmHg, N = 7) and anesthetized rats (from 123 ± 6.9 to 87 ± 8.7 mmHg, N = 7) when lidocaine (34 nmol/200 nl) was microinjected into the RVLM. The heart rate variations were not consistent and only eventually reached significance in conscious or anesthetized rats. The right position of pipettes was confirmed by histology and glutamate microinjection into the RVLM. These findings suggest that in conscious animals the RVLM, in association with the other sympathetic premotor neurons, is responsible for the maintenance of sympathetic vasomotor tone during bilateral RVLM inhibition. Activity of one or more of these premotor neurons outside the RVLM can compensate for the effects of RVLM inhibition. In addition, the effects of lidocaine suggest that fibers passing through the RVLM are involved in the maintenance of blood pressure in conscious animals during RVLM inhibition.

Fatigue studies of isolated, intact muscles typically utilize solutions saturated with O2. However, under in vivo fatiguing conditions, less oxygen is delivered to the muscles and they actually experience hypoxia. No studies to date have correlated the effects of acute hypoxia on the isometric contractile properties of intact muscles, skinned fibers isolated from the same muscles, and the cellular content of specific muscle proteins. Therefore, we have studied the effects of in vitro acute hypoxia on the fatigability of intact diaphragm muscle strips and on the isometric contractile properties of single Triton-skinned fibers isolated from control and hypoxic diaphragm muscles. We found that hypoxia and fatiguing stimulation per se affect the tetanic force of intact muscle strips without exhibiting any significant deleterious effects on the calcium-activated force of skinned muscle fibers dissected from the intact muscles. In contrast, fatiguing stimulation under hypoxic conditions decreased both the tetanic force of muscle strips and the calcium-activated force of skinned muscle fibers. Gel electrophoresis of muscles subjected to hypoxia and hypoxic-fatigue revealed that there is a significant reduction in three protein bands when compared to control muscles. Protein modification may be the underlying mechanism of muscle fatigue under physiologic conditions.

Insulin-like growth factors (IGFs) are important regulators of epithelial cell growth. The mitogenic activity of these factors is influenced by the levels of extracellular IGF binding proteins, including insulin-like growth factor binding protein 3 (IGFBP-3). In the present report we study the effects of epidermal growth factor (EGF) and all-trans-retinoic acid (RA) on IGFBP-3 RNA and protein levels in human papillomavirus-immortalized cervical epithelial cells. Treatment of ECE16-1 cells with 3-20 ng/ml EGF causes a marked reduction in IGFBP-3 levels. In contrast, 1 microM RA increases IGFBP-3 mRNA and protein levels in the presence or absence of 20 ng/ml EGF. The response is concentration dependent with a half-maximal increase observed at 1 nM RA. RA is able to reverse the EGF suppression when added simultaneously or 3 days after initiation of EGF treatment. Conversely, when cells are treated with RA, IGFBP-3 levels increase within 24 h and subsequent addition of EGF is without effect. Thus, the RA-dependent increase in IGFBP-3 levels is dominant over the EGF suppression. The increased IGFBP-3 levels are correlated with RA suppression of proliferation. Similar RA effects on IGFBP-3 mRNA levels were observed in other cervical epithelial cell lines (i.e., ECE16-D1, ECE16-D2, and CaSki). These results suggest that RA may act to inhibit cervical cell growth by increasing IGFBP-3 levels and reducing the extracellular concentration of free insulin-like growth factor I (IGFI) and/or alternatively, IGFBP-3 may inhibit cell growth by direct effects on the cell, independent of IGFI.

Vasopressin acts at a number of sites in the central nervous system to alter arterial pressure. This study investigated the hypothesis that vasopressin acts at the rostral ventrolateral medulla to increase arterial pressure. The rostral pressor area of the medulla oblongata was exposed in urethane-anesthetized rats prepared for topical application of vasopressin. A 3-minute application of vasopressin (range 10"* to 10" 3 M) produced dose-dependent increases in arterial pressure that averaged between 2±1 and 65±11 mm Hg (p<0.01). Tachycardia was not a consistent response at any concentration of vasopressin. Intravenous administration of a V, vasopressin antagonist did not modify the pressor response produced by topical application of vasopressin (10 M). Application of the Vi antagonist to the rostral pressor area, however, prevented the production of a pressor effect to subsequent topical application of vasopressin (10~4 M). These experiments suggest that vasopressin stimulates the activity of vasomotor neurons in the rostral ventrolateral medulla by a mechanism that involves a neuronal V, receptor. (Hypertension 1990;15(suppl I):I-102-I-106) C urrently, the role of neuropeptides in the central control of blood pressure is the subject of considerable attention. It has been shown that intracerebroventricular injections of angiotensin II (Ang II), vasopressin (VP), substance P, and enkephalin increase blood pressure. To better understand the pathways that can account for the effects produced by intracerebroventricular injection of peptides, we focused our attention on the ventrolateral medulla (VLM) because it plays an important role in the regulation of blood pressure. We showed that topical application of Ang II at a region overlying the rostral ventrolateral medulla (RVLM) increases blood pressure without producing changes in heart rate.1 The ventral medulla receives a projection of VP-containing fibers originating in the paraventricular nucleus of the hypothalamus.2 Additionally, high affinity binding sites for VP have been demonstrated recently in the vicinity of the VLM.3 Thus, we investigated the cardiovascular effect of VP applied topically to the rostral ventral medullary surface of the rat. (1.5-1.8 g/kg i.v.). Studies were conducted according to the guidelines set forth by the American Physiological Society. The trachea was cannulated and the rat permitted to breathe spontaneously. With the rat in a supine position, the head was fixed in a stereotaxic frame. The ventral aspect of the medulla was exposed as described by Feldberg and Guertzenstein. 4 A femoral artery and vein were cannulated to monitor arterial pressure and to administer drugs and fluids, respectively. Peptides were diluted in saline (pH 7.4) and applied topically to both sides of the RVLM by means of Gelfoam pledgets (1 mm 2 ). Pledgets were saturated in 1 y\ solution of the peptide and positioned rostral to the hypoglossal nerve rootlets and lateral to the border of the pyramidal tract. In some experiments, the correct placement of the p...