I did a VIN search and its

I did a VIN search and its not as easy to get normals as one would see in the dog or cat. Her is a reference from Tom Donnely:

Dimensions are not given of adrenal glands in the literature. Researchers/anatomists give weights or organ weight to body weight ratios. Researchers have emphasized that weights and measurements of lungs, thyroids and adrenals are extremely variable in guinea pigs. Interestingly there are two distinct spleen shapes, a long narrow type in most guinea pigs, and a short stubby type in selected inbred guinea pig lines. 

The left adrenal gland is bigger. The left adrenal gland is in contact with the renal vessels, while the right is not. Gensicke (1996) in a German thesis (Quantitativ-morphologische Untersuchungen an Herzen, Nieren und Nebennieren von normalen Meerschweinchen im Alternsgangand) recorded absolute weights of 0.55 ± 0.19 gm in male guinea pigs and 0.42 ± 0.31 gm in females (age range 7-26 months; n=40). Sexual dimorphism of the adrenal gland weight occurs at puberty in guinea-pig – this dimorphism is suppressed by castration in male or injection of testosterone in female. Earlier reports found the adrenal gland increases its own weight as body weight (> 500 g) increases. A striking example is when guinea pig body weight increases 100% (from 500 g to 1 kg) – the adrenal gland increases in weight by 245% (Mixner et al. 1943. Relation of certain endocrine glands to body weight in growing and mature guinea pigs. Endocrinology 23(1): 298-304). 

A lot of research has been conducted on guinea pigs to look at effects of social isolation in young and subsequent behavior, or behavior in guinea pigs from stressed mothers (during lactation and pregnancy). Significantly higher adrenal weight occurs in daughters (not males) of mothers exposed to unstable social environments in during pregnancy and lactation. In males, social isolation has no effect if the males remain isolated; but put the socially isolated reared males in a mixed social group, and the isolated males show tremendous increase in adrenal size and die after 3-5 days (it’s a situation similar to Antechinus, a Australian dasyurid marsupial during breeding season when all the males die). 

So although we can give adrenal weights of socially stable, disease free guinea pigs with age, adrenal weight (and size) will vary with whether guinea pig is inbred or outbred, and will vary depending on social environment. 

Tom

Thomas M Donnelly, BVSc, DipACLAM,ABVP(ECM),ECZM(SM) 
École Nationale Vétérinaire d’Alfort 
Maisons-Alfort, France

I also took a screen shot stating the adrenal gland in the guinea pig can be nearly 1/3 the size of the kidney at times.

I’m not sure you can make any generalizations about the guinea pig. I guess you need to go back to what EL has to say- does it meet the criteria of “curvi-linear”. If so- maybe it is normal.