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

Summary

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.