Technique for placement of chronic third cerebroventricular cannula in female goats (Capra hircus).

A practical method for chronic catheterization of the third cerebroventricular space in goats was developed by using a stereotaxic device. In female goats of various ages and weights, a stereotaxically mounted drill was positioned at an angle of 11.5 degrees with the tip of the drill bit located at a skull reference point 2 to 3 mm rostral to the posterior border of Bregma (intersection of the coronal with the sagittal sutures). The hole that was drilled served as the guide for a tight-fitting cannula, which was 20-gauge stainless steel with a stylet. The cannula was advanced by hand to a depth of approximately 40 mm from the top of the skull, positioning the cannula tip in the anterior region of the third ventricle anterior to the massa intermedia. Copious flow of cerebrospinal fluid verified appropriate positioning. The cannula was anchored with dental acrylic and a subcutaneous port system attached via plastic tubing. Cannula placement was assessed after surgery by use of fluoroventriculography. Cannula patency was maintained for 23 months. Minimal complications were seen, maintenance was minimal, and animals were allowed complete freedom of movement with no requirement for jackets or wraps and were used in several consecutive studies. No anesthetic complications were noticed.

Effect of inspiratory-phase negative pressure breathing on urine flow in man.

We investigated the effect of negative pressure breathing during the inspiratory phase only (intermittent NPB) in 9 healthy male subjects who were in a sitting position and had no food or fluid intake for 12 h before the study. Intermittent NPB was without effect on urine flow and urinary sodium excretion but caused a significant increase in creatinine clearance. Plasma renin activity was significantly reduced, whereas plasma antidiuretic hormone (ADH), atrial natriuretic factor (ANF), and aldosterone levels were unaffected. To determine whether the blunted urinary response to intermittent NPB was a postural phenomenon, the study was repeated in 6 of the subjects while supine. Under these conditions there was a significant increase in urine flow and plasma ANF levels, but no change in all other measured variables. These results are consistent with a role for ANF, but not ADH, in the diuresis seen in supine subjects during NPB.

Differential ontogeny of in vitro vascular responses to three categories of calcium channel antagonists in rats.

We examined the ontogeny of relaxation responses to three categories of calcium channel antagonists, represented by verapamil, diltiazem, and nifedipine, for both potential-operated (KCl-mediated) and receptor-operated channels [norepinephrine (NE)-mediated] in rat thoracic aorta. Aortic rings from 2- to 3-d, 1-wk, and 12-wk-old Sprague Dawley rats were mounted in an organ bath, bathed in Krebs' solution, and connected to a force-displacement transducer to measure isometric tension. Endothelium intact vessels at optimal passive force were exposed to a single ED50 of isotonic KCl or NE, equilibrium contraction was measured, then vessels were washed and exposed for 30 min to 1 microM verapamil, 1 microM diltiazem, or 0.1 microM nifedipine, followed by another dose of KCl or NE. Verapamil and diltiazem demonstrated significant (p less than 0.05) age-related increases in effectiveness for blocking KCl-mediated contraction [(% reduction of control contraction +/- SEM) (Verapamil: 2-3 d, 67.7 +/- 4.2; 1 wk, 72.5 +/- 1.8; 12 wk, 89.5 +/- 1.0. Diltiazem: 2-3 d, 64.6 +/- 2.9; 1 wk, 73.5 +/- 3.0; 12 wk, 83.1 +/- 1.8]. Nifedipine was equally effective at all ages: 2-3 d, 85.6 +/- 1.3; 1 wk, 90.0 +/- 1.6; and 12 wk, 91.3 +/- 1.4. Verapamil and diltiazem also showed significant age-related increases in effectiveness for blocking NE-mediated contraction (Verapamil: 2-3 d, 6.2 +/- 3.9; 1 wk, 28.0 +/- 4.8; 12 wk, 44.1 +/- 6.0. Diltiazem: 2-3 d, 8.0 +/- 3.1; 1 wk, 20.5 +/- 3.9; 12 wk, 46.5 +/- 4.8).(ABSTRACT TRUNCATED AT 250 WORDS)

Ontogeny of vasoconstrictor neurohypophysial hormone function in rats.

This in vitro study examined the ontogeny of arginine vasopressin (AVP) and arginine vasotocin (AVT) compared with norepinephrine (NE)-mediated contraction in rat thoracic aortas. Aortas from three age groups (2-3 days, 6-7 days, and 12 wk) of Sprague-Dawley rats were used. Ring segment resting length was adjusted to optimize tension developed to a dose that produces half-maximal tension of NE in Krebs solution (pH 7.4, 37 degrees C) and gassed with 95% O2-5% CO2. Cumulative dose-response curves were generated for KCl (5-100 mM), NE (10(-10)-10(-5) M), AVP, and AVT (both 10(-10)-10(-6) M) in the presence and absence of a selective V1 vasopressinergic inhibitor, [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-(O-methyl)tyrosine]arginine vasopressin ([d(CH2)5Tyr(Me)]AVP). A progressive increase in sensitivity among all age groups was found for KCl and NE. There was a slight decrease in sensitivity to both AVP and AVT in the 1st wk. Maximum contractile response to NE increased between 2-3 and 6-7 days, whereas no change was observed for KCl, AVP, or AVT. AVP- and AVT-mediated contractions were selectively inhibited by [d(CH2)5Tyr(Me)]-AVP. These results suggest 1) receptor-mediated contractility is present from 2 days of age for NE, AVP, and AVT; 2) sensitivity to KCl and NE increases progressively during postnatal development, whereas sensitivity to AVP and AVT slightly decreases in the 1st wk with no progressive age-related increase by 12 wk; 3) AVP and AVT mediate contraction via a similar V1-like receptor.