A Morphological and Histological Examination of the Pan‐tropical Spotted Dolphin (Stenella attenuata) and the Spinner Dolphin (Stenella longirostris) Adrenal Gland

Abstract

The morphology and histology of the cetacean adrenal gland are poorly understood. Therefore, this study examined 32 pairs of adrenal glands from 18 pan-tropical spotted dolphins (Stenella attenuata) and 14 spinner dolphins (Stenella longirostris). In both species, the cortex was pseudolobulated and contained a typical mammalian zonation. Medullary protrusions (0-3 per section) and a medullary band were identified in both species. For S. attenuata, no statistical differences were found in the cortex to medulla (CM) ratio or the percent cross-sectional area (PCA) of the adrenal glands compared with sex or sexual maturity. The mean CM ratio for S. attenuata was 2.34 and the PCA was 64.4% cortex, 29.4% medulla and 6.2%'other'. 'Other' indicates blood vessels, connective tissue and the gland capsule itself. For S. longirostris, there was no statistical difference in the CM ratio compared with sexual maturity. However, a statistical difference was found between the CM ratio and sex, suggesting sexual dimorphism (female CM ratio = 2.46 and males = 3.21). No statistical differences were found in the PCA of S. longirostris adrenal glands by sexual maturity. However, a statistical difference was found between the PCA by sex. Female S. longirostris adrenal glands consisted of 65.0% cortex, 27.3% medulla and 7.7% 'other', whereas male adrenal glands consisted of 71.7% cortex, 22.7% medulla and 5.6% 'other'.

Histological Structure of the Adrenal Gland of the Bottlenose Dolphin (Tursiops truncatus) and the Striped Dolphin (Stenella coeruleoalba) from the Adriatic Sea

“…However, in the adrenal glands of the bottlenose dolphin and striped dolphin studied, connective tissue trabeculae extended to the layer of connective tissue between the cortex and the medulla and then spread as very thin septa through the entire medulla. A similar arrangement of connective tissue within the adrenal gland was described for different whale species by Simpson and Gardner (1972) and Clark et al (2005, 2008).…”

“…The zona glomerulosa is found in humans and bovids whereas the zona arcuata is described in horses, donkeys, carnivores and pigs (Banks, 1993; Dellmann, 1993; Raviola, 1994; Junqueira and Carneiro, 2005). In marine mammals, examined so far, the adrenal cortex is also divided into the zona glomerulosa, the zona fasciculata and the zona reticularis (Simpson and Gardner, 1972; Zhongjie, 1988; Bragulla et al., 2004;Clark et al, 2005, 2008). It seems that there are significant differences in zone thickness in different marine mammal species, which may be related to the functional state of the gland (Simpson and Gardner, 1972).…”

“…Pseudolobulation was described in various species of cetaceans (Zhongjie, 1988, Lair et al, 1997; St. Aubin, 2002; Clark et al, 2005, 2008); however, it seems that it was not found in pinnipeds (Simpson and Gardner, 1972). The degree of pseudolobulation of the adrenal cortex in the pan‐tropical spotted dolphin and the spinner dolphin varied from minimal to highly lobulated (Clark et al, 2008).…”

“…Aubin, 2002; Clark et al, 2005, 2008); however, it seems that it was not found in pinnipeds (Simpson and Gardner, 1972). The degree of pseudolobulation of the adrenal cortex in the pan‐tropical spotted dolphin and the spinner dolphin varied from minimal to highly lobulated (Clark et al, 2008). Lucić (2002) found stronger lobulation of the adrenal cortex in the bottlenose dolphin than in the striped dolphin from the Adriatic Sea.…”

Histology and Histochemistry of the Adrenal Gland African Giant Rat (Cricetomys gambianus, Waterhouse)

“…Moreover, in horses, cows, sheep and pigs, the medulla is divided into two areas, the outer area, made up of the more intensively stained epinephrine-secreting cells, and the inner area, built of norepinephrine-secreting cells that have a weaker stain affinity (Dellmann). The absence of connective tissue separating the adrenal cortex and the medulla in the African giant rat is at variance with what obtains in the dolphins and harbor seal male (Clark et al, 2008).…”