Morphology of the rectal gland of the spiny dogfish (Squalus acanthias) shark in response to feeding

The morphology of the rectal gland was examined in spiny dogfish (Squalus acanthias L, 1758) sharks fasted (I week) or 6 and 20 h postfeeding The morphology of the fasted gland showed a pattern reflecting a dormant physiology, with thick gland capsule, thick stratified epithelium, and secretory parenchyma with tubules of small diameter and lumen. The secretory cells of the tubular epithelium were enlarged and irregularly shaped with abnormally condensed or highly vacuoiized cytoplasm containing numerous lysosomes. Early-stage apoptotic cells were not uncommon. Secretory cells showed signs of low activity, e.g., mitochondria with weakly stained matrix and small cristae, poorly branched in foldings of basolateral membranes, and microvesicle-free subapical cytoplasm. All characteristics examined changed significantly upon feeding, consistent with increased salt and fluid secretion: the outer capsule muscle layer and the strati lied epithelium decreased in diameter; the tubules enlarged; the secretory cells showed extensive development of the basolateral membrane, more mitochondria, and abundant apical micro vesicles. Secretory cell apical surface was increased. The minor differences between morphology in 6 and 20 h postfeeding indicated that changes took place rapidly and were complete by 6 h. Our results are discussed in the context of prior studies of metabolism, proteomics, and cellular pathways of gland activation.