The effects of acute starvation on parotid acinar cells. Ultrastructural and cytochemical observations on Ad Libitum‐fed and starved rats

Abstract

Parotid acinar cells from ad libitum-fed and starved rats were studied using electron microscopic and cytochemical techniques. Lysosomes containing acid phosphatase and non-specific esterase activity were present in cells of both ad libitum-fed and starved rats. They included lipofuscin-like bodies, smaller round or irregularly-shaped bodies, multivesicular bodies, and coated vesicles. After 16-24 hours of starvation, lipid droplets had accumulated in the basal cytoplasm, and secretory granules showed evidence of degeneration. These altered granules consisted of irregular clumps of dense material in a less dense matrix. After 48-72 hours of starvation, the altered granules increased in number and fused to form large aggregates. Some of the aggregates also contained vesicles, membranous material, and lysosomal residues. The altered granules and aggregates were reactive for acid phosphatase and non-specific esterase. The formation of the altered granules appeared to occur by spontaneous degeneration of the secretory granules, with secondary fusion with pre-existing lysosomes and other altered granules. The results suggest that the lysosomal system of the parotid acinar cell functions to segregate and digest secretory granules during periods of reduced secretory stimulation.Previous studies have demonstrated that the structure and enzyme content of the rat parotid gland are dependent upon food intake and consistency. In normal animals, the nocturnal eating habits produce a diurnal variation in gland weight and secretory protein content (Sreebny and Johnson, '69). Starvation eliminates the diurnal variation and causes a reduction in gland weight and amylase content beginning after one day of starvation (Johnson and Sreebny, '71). In rats maintained on a liquid diet (Metrecal or liquified pellets), parotid acinar cells undergo atrophy, with a decrease in gland weight, amylase and RNA content and loss of the diurnal variation (Hall and Schneyer, '64, '69; Johnson and Sreebny, '71 ) The present study was undertaken because information regarding morphological changes during the early stages of reduced glandular function is lacking. In order to study these changes parotid glands from ad libitum-fed rats and rats starved for 16-72 hours were examined by electron microscopy, with special reference to the identification of lysosomes and the distribution of two lysosomal enzymes, acid phosphatase and non-specific esterase. The results indicate that lysosomes containing acid hydrolase activity are present in parotid acinar cells of normal as well as experimental animals. During starvation, the acinar cells accumulate lipid droplets, and some of the secretory granules show morphological and cytochemical alterations suggestive of degeneration. The evidence presented here suggests that one of the functions of the lysosomal system 71 72 ARTHUR R. HAND in the parotid acinar cell is segregation and digestion of secretory granules when the stimulus for their normal discharge from the cell is removed. MATERIALS AND METHODSAdu...

Biosynthesis of a Salivary Bacteria-Agglutinating Glycoprotein in the Rat during Protein Deficiency

“…During protein deficiency the biosynthesis of bio logically active agglutinin is reduced. This is compatible with the severe morphologi cal changes which have been found in the submandibular [Enwonwu, 1972] and pa rotid [Hand, 1972] glands of the rat during severe protein-energy deficiency, 0.5% protein diet and total starvation, respec tively. Fragmentation and dilatation of the endoplasmic reticulum and pronounced disaggregation of the polyribosomes were found as well as large lipid bodies, cyto plasmic vacuoles and small abnormal se cretory granules.…”

“…The total counts in the saliva samples from the two dietary groups were similar, but saliva from the deficient rats contained a lower amount of labelled glycoproteins adsorbable to the bacteria. We conclude that the total amount of glycoprotein synthetized during the experimental 2-hour period is not changed whereas the synthesis of biologi cally active agglutinin is decreased.Severe protein-energy malnutrition (PEM) reduces the size of both the parotid [Johnson et al, 1977;Ericson et al, 1984] and the submandibular glands [Enwonwu, 1972;Ericson et al, 1984], Degenerative changes of the subcellular organelles [En wonwu, 1972;Hand, 1972] and reduced contents of RNA and DNA [Menaker and Navia, 1973;Johnson, et al, 1977] in sali vary glands are reported. During PEM a reduced transcription activity from nuc lear DNA in liver cells was observed Decken et al, 1981] indi cating impairment of protein synthesis during protein deficiency.…”

Intracellular localization of acid phosphatase and trypsinogen on an identical specimen in rat pancreas.

“…One of the roles of the lysosomes in secretory cells might be to degrade endogenous secretory products when the discharge of the products is depressed under certain physiological conditions (7,22). Ikehara et al (10) reported that proalbumin was converted to albumin in secretory vesicles of rat liver and almost the same results have reported by Quinn et al (19).…”

alpha‐Adrenergic, beta‐adrenergic and cholinergic mechanisms for amylase secretion by rat parotid gland in vitro.

“…B). Lipid droplets and, occasionally, degenerated secretary granules similar to those suggested by Hand (1972) to result from starvation, were often found in the basal portion of acinar cells. The complete secretion cycle of the parotid acinar cell (exocytosis of granular material and its resynthesis) induced either by injection of a fiadrenergic agonist (Amsterdam et al 1969;Simson, 1969;Cope & Williams, 1973), or by sympathetic nerve stimulation (Garrett & Thulin, 1975) in vivo has been thoroughly documented.…”