Effects of Exogenous Thyroid Hormone on the Postnatal Morphogenesis of the Rat Parotid Gland

Abstract

Administration of thyroid hormone has been shown to accelerate the early postnatal development of the rat parotid gland, but these studies have dwelt almost entirely on biochemical changes. The objective of this study was to describe the effects of exogenous thyroid hormone on morphologic aspects of the developing parotid gland, in particular the transient appearance of scattered mucous cells in this otherwise serous gland. Pups were given a daily subcutaneous injection of thyroxine (T(4)) of 0.1, 0.5, or 5.0 microg/g body weight, vehicle only (injection control), or no injection (normal control) beginning at 4 days, and killed for the collection of blood and parotid glands at intervals through 15 days. The serum was analyzed for T(4) and the glands were examined by light and electron microscopy. The results indicated that both serum T(4) and the pace of gland development were proportional to the dose of T(4). In particular, T(4) accelerated decreases in acinar size and gland area occupied by stroma and translocation of a subset of cells with small secretory granules, deeply stained with periodic acid-Schiff, from acini to intercalated ducts. However, the chronology of mucous cell disappearance was indifferent to treatment. In addition, signs of toxicity, including slower gain in body weight and greatly increased apoptosis and vacuoles in the glands, occurred with the higher doses of T(4).

Morphologic diversity of the minor salivary glands of the rat: fertile ground for studies in gene function and proteomics

“…The glands are embedded in the submucosa and skeletal muscles of the posterior dorsum and lateral borders of the tongue, one group surrounding the single vallate papilla, and two other groups Stensen's duct upstream from this junction to avoid contamination by mucous secretions and 2) their development suggests that there could be similarities between the glands that might plausibly be related to their origin from the same anlage. Interestingly, scattered mucous acinar cells with biphasic secretory granules very similar to those of the anterior buccal gland occur transiently in the developing parotid gland during the fi rst few days after birth (Taga and Sesso 1979, Ikeda and Aiyama 1997, Ikeda et al 2007). These mucous cells reacted moderately to strongly with the anti-SL antibody (Fig.…”

“…Archival series of serial frontal and transverse paraffi n sections of the heads and tongues of Sprague-Dawley rats ( Rattus norvegica albinus ) from previous studies Sreebny 1971, Redman 1972) and sections of parotid glands from 7-day-old rats (Ikeda et al 2007) were re-examined. These were supplemented with tissue samples from male and female young adult (age 50 Ϯ 5 days), Sprague-Dawley rats (certifi ed viral pathogen free) obtained from Charles River, Raleigh, NC and Harlan, Indianapolis, IN, and these were housed in the Animal Research Facility of the Washington, DC, Department of Veterans Affairs Medical Center.…”

Effects of glucocorticoid on postnatal development of rat sublingual glands

“…The thyroid hormone thyroxin (T 4 ) and androgens both promote differentiation of the granular ducts of the submandibular glands, and early production of epidermal growth factor (EGF) and nerve growth factor (NGF) (Chabot et al, 1987, Gresik et al, 1981, Bray et al, 1982. T 4 has also been shown to exert a stimulatory influence on postnatal development of the parotid glands (Ikeda et al, 2007). In utero administration of glucocorticoids, which are adrenocortical steroid hormones, promotes division of the epithelial strands of the submandibular glands, and induces early appearance of mucin in acinar cells (Jaskoll et al,1994, Jaskoll et al,1998.…”

Exogenous thyroid hormone affects myoepithelium and proliferation in the developing rat parotid gland

“…This permits the study of factors that influence gland development via interventions applied directly to the pups, thus avoiding modifications of the effects of application via the dams. Alterations of diet and hormones have been shown to influence strongly postnatal development of rodent salivary glands (Sasaki et al 1976, Takeuchi et al 1977a,b 1978, Takuma et al 1978, Kumegawa et al 1980, Johnson 1987, Ikeda et al 2008, Inukai et al 2008). Serum thyroid hormone concentration is low in the perinatal rat, increases to twice the adult level by 16 days of age, and returns to the adult level by 30 days (Clos et al 1974, Porterfield and Hendrick 1981, Dussault et al 1982, Porterfield 1985, Farwell and Dubord-Tomasetti 1999).…”

“…During postnatal development, however, these cells differentiate around both intercalated ducts and acini, then translocate to only intercalated ducts during weaning (Redman et al 1980, Tsujimura et al 2006). Previously, we found that exogenous thyroxine (T 4 ) accelerates the translocation of cells with small secretory granules from acini into intercalated ducts, and apoptotic cells increased tremendously with high doses (Ikeda et al 2008). We present here further analysis of parotid glands to determine the effects of T 4 on the distribution of MEC and proliferation of parenchymal cells in the developing rat parotid gland during the two weeks after birth.…”