Salt gland blood flow in saltwater-adapted Pekin ducks: Microsphere measurement of the proportionality to secretion rate and investigation of controlling mechanisms

Abstract

The relationship between blood flow and secretion in the salt glands of conscious saltwater-adapted Pekin ducks has been investigated using intraventricular injection of radioactively labeled microspheres to measure capillary flow. 1. During steady state secretion driven by continuous i.v. infusion of 1,000 milliosmolal NaCl, salt gland blood flow,\(\dot Q_w (ml \cdot \min ^{ - 1} \cdot g \cdot ^{ - 1} )\), is proportional to the rate of solute secretion,\(\dot S\), from 0 to 0.9 mOsm·min−1: $$\dot Q_w = 28 \times \dot S + 0.7,r = 0.82$$ (Fig. 3, closed circles). 2. Alpha-adrenergic blockade with phenoxybenzamine, though significantly increasing myocardial blood flow by more than 50%, dose not alter either resting salt gland blood flow nor the proportionality between blood flow and secretion (Fig. 4). 3. Ongoing secretion and the elevated salt gland blood flow are both decreased by atropine (Fig. 5), but the blood flows in atropine-inhibited salt glands (Fig. 3, open circles) are 3–6 fold higher than flows in ducks not receiving a salt load. 4. The slope of the regression line relating salt gland blood flow and secretion rate during transient secretory responses (Fig. 6) is parallel to the steady state regression line, but shows a significant vertical offset. 5. Our results indicate that salt gland blood flow is closely linked to secretion rate, with only a small component of the increased blood flow in active salt glands independent of secretory activity.