Evaporative Cooling in the Rat: Differences Between Salivary Glands as Thermoregulatory Effectors

Abstract

Rats cool themselves in the heat by evaporating saliva groomed onto their body surfaces. Previous reports indicated that surgical removal of the submaxillary glands severely impaired evaporative water loss and body temperature regulation, whereas parotid desalivation had little effect. In the present experiments saliva was collected directly from the oral cavities of rats exposed to heat stress and was identified by its sodium concentration to determine the roles of individual salivary glands as thermoregulatory effectors. The fundamental difference between the glands was that submaxillary secretion was initiated at a lower level of hyperthermia (38.5 °C) than parotid secretion (40.0 °C), and thus made a greater contribution to thermoregulation. For example, normal rats secreted only submaxillary saliva at an ambient temperature of 36 °C and secreted three times more submaxillary saliva than parotid saliva at 40 °C. These results indicate that the submaxillary glands are primary thermoregulatory effectors of rats during heat stress, and that the parotid glands provide supplementary secretion only during pronounced hyperthermia.

Renin‐like activity of the rat submaxillary gland: characterization and the effect of several drugs and stimuli

“…It is noteworthy that the submaxillary gland is of major importance in the rat for functions other than digestion, as, for example: heat regulation, which involves loss of considerable volumes of saliva, smeared on the fur (Hainsworth & Stricker, 1971) or water intake induced by hypovolemia (Gutman & Benzakein, 1969). Interestingly, both tissues which contain renin activity, the kidney and the submaxillary gland, are essential for thirst induced by hypovolemia (Gutman & Benzakein, 1969;Gutman et al, 1971) and the renin-angiotensin system has been demonstrated to be a thirst-inducing stimulus (Fitzsimons & Simons, 1969).…”

Circumventricular Organs: Gateways to the BrainMultisynaptic Neuronal Pathways From The Submandibular And Sublingual Glands To The Lamina Terminalis In The Rat: A Model For The Role Of The Lamina Terminalis In The Control Of Osmo‐ And Thermoregulatory Behaviour

“…dogs using open‐mouth panting), the salivary glands of rats, especially the submandibular and the sublingual glands, function under certain physiological conditions (e.g. heat stress) as thermoregulatory heat loss effector organs 1 . Salivation is the autonomically controlled component of otherwise complex thermoregulatory responses engaged in dissipating body heat by evaporative water loss used by several mammalian species.…”

“…Instead, they activate other heat loss mechanisms, such as skin vasodilation, especially of the tail, and they also salivate and spread the saliva on their skin and fur to remove heat by evaporation. For saliva spreading, the submandibular and the sublingual glands are primary thermoregulatory effector organs under such conditions 1 . Saliva lost under heat stress has implications for the body fluid economy of the rat and contributes to thermal dehydration and subsequent thirst 2–4 .…”

The median preoptic nucleus is involved in the facilitation of heat-escape/cold-seeking behavior during systemic salt loading in rats

“…Under general an anesthesia induced by an intraperitoneal injection of pentobarbital sodium (Nembutal, 50 mg/ kg; Dainippon, Osaka, Japan), the salivary ducts of the parotid and major sublingual and submaxillary glands were bilaterally ligated, and the glands were removed to minimize active evaporative heat loss. It has been reported that the submaxillary gland is the most important for evaporative heat loss in the heat (10). As reported in our previous study (32), rats without these major salivary glands could not control their body temperature during a heat exposure at 40°C.…”