Secretory capacity of the lachrymal salt gland of hatchling sea turtles,Chelonia mydas

Summary

The lachrymal salt glands ofChelonia mydas were functional when hatchlings emerged from the nest. Osmotic concentrations up to 720 mosmol kg⁻¹ were recorded in spontaneously produced tears (salt gland secretions). When injected with a Na⁺ load (1500–2700 μmol (100 g)⁻¹) newly emerged hatchlings produced tears ranging in osmotic concentration from 1000–1900 mosmol kg⁻¹ with Na⁺ secretion rates from single glands of 200–475 μmol (100 g·h)⁻¹. In these circumstances the rate of sodium excretion, via the salt glands, was equivalent to the sodium content of 0.2 to 0.5 ml of sea water per hour. Since the apparent drinking rate of hatchlings within the first two days of entering sea water was approximately 0.5 to 1.7 ml per day, the excretion of Na⁺ imbibed by drinking is well within the secretory capacity of the lachrymal salt glands.

In feeding hatchlings extraordinarily high Na⁺ secretion rates were induced by Na⁺ loading. Hatchlings which were loaded with Na⁺ by injection (1500–5400 μmol (100 g)⁻¹) produced tears having osmotic concentrations between 1500 and >2000 mosmol kg⁻¹. The Na⁺ secretion rates from single glands were 750–4185 μmol (100 g·h)⁻¹ with extremely high short term rates of 10700 μmol (100 g·h)⁻¹ (50 μmol min⁻¹ for 28 g hatchlings).

In terms of gland mass the highest long term secretion rate translates into 21 mmol of Na⁺ per gram of salt gland per hour and is the highest secretion rate yet recorded for a reptilian salt gland. This rate is almost three times the highest rate recorded for sea snakes (8 mmol g·h⁻¹) and is similar to rates commonly observed in avian salt glands (25 mmol g·h⁻¹).

Secretion by the lachrymal salt glands was initiated by increased blood concentrations of Na⁺ or K⁺, K⁺ being as effective as Na⁺ but with the composition of the teras being virtually unchanged compared to tears from Na⁺ stimulated hatchlings. Preliminary experiments indicated that secretion was not initiated by increased Cl⁻ concentration in the blood or by increased volume or osmotic concentration of the blood.