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Determination of parotid sulfate secretion in sheep by means of ultrasonic flow probes¹

F. Méot^*, J.-M. Bonnet^*, R. Boivin^* and A. Cirio^,2

^* Unité de Physiologie, Pharmacodynamie et Thérapeutique, Ecole Nationale Vétérinaire de Lyon, F69280 Marcy L’Etoile, France; and and Departamento de Fisiología, Facultad de Veterinaria, Montevideo 11600, Uruguay

² Corresponding author: cirio{at}montevideo.com.uy

The bilateral output of sulfate in parotid saliva, the relationship with its plasma level and with parotid flow, and its variation according to feeding behavior were determined in ad libitum, normal-sulfate (0.28% DM)-fed sheep (n = 6) using a transit time ultrasonic flow meter system to measure salivary flow. Ultrasonic flow meter probes were bilaterally implanted, under general anesthesia, around parotid ducts previously fitted through their oral ends with nonobstructive sampling catheters. Salivary flows were continuously recorded during 24 h, and saliva and blood samples for sulfate determinations were obtained hourly. Jaw movements were monitored with the submandibular balloon technique. The sulfate concentration in parotid saliva (mean of the group = 4.9 ± 3.7 µg/mL) showed high variability between sheep (individual means from 0.4 ± 0.3 to 9.3 ± 5.9 µg/mL) and averaged 12.3% of the more stable plasma level (41.2 ± 8.1 µg/mL). Pronounced intraindividual variations were also evident (0.1 to 26.3 µg of sulphate/mL of parotid saliva), in strong association with the fluctuations of salivary output. In 4 sheep, a decreasing exponential relationship was observed between parotid sulfate concentration and salivary secretion rate (r² = 0.36, P < 0.01). This fact and the absence of a relationship between sulfate levels in plasma and in saliva suggest a sulfate secretory process during the passage of primary saliva through the ductal tree of the gland. The greatest rates of bilateral salivary sulfate output were observed during feeding (14.1 ± 14.0 µg/min) and rumination (12.7 ± 11.0 µg/min). Nevertheless, 49% of the sulfate output in parotid saliva was present during rest, as a result of the length of the resting times. The contribution of parotid sulfate to the ruminal S pool was highly variable and averaged 13.2 mg/d, representing less than 1% of the S intake. In conclusion, the accurate, reliable, nonobstructive, and bilateral salivary flow monitoring, using a previously characterized ultrasonic flow meter technique, allowed a detailed determination of the secretory dynamics of sulfate in parotid saliva, without disturbing the animal’s routine or altering the physiological regulation of salivary output. The results indicated that, in the absence of S deficiency, the recycling of sulfate via saliva seems not to be a major factor in sheep nutrition.

Key Words: feeding behavior • parotid saliva • sheep • sulfate secretion • ultrasonic device