Serum prolactin and macroprolactin levels in diabetic nephropathy

Three molecular forms of prolactin with molecular weights of 23 (monomeric), 50 - 60 and > 100 kDA (macroprolactin) have been defined. Prolactin levels have been shown to be reduced in especially poorly controlled diabetes mellitus and the prevalence of macroprolactinemia in diabetic patients has been higher than the non-diabetic population.

A total 234 Type 2 diabetic patients with different nephropathy stage was included in the study. Serum prolactin levels were analyzed by the Electrochemiluminescense method. Following polyethylene glycol (PEG) precipitation, recovery less than or equal to 40% was taken as evidence that a significant level of macroprolactin was present in the serum.

Hyperprolactinemia and macroprolactinemia were detected in 40 (17%) and 13 (5.5%) patients, respectively. Macroprolactinemia was detected 13 of 40 patients with hyperprolactinemia (32.5%). Increased prolactin and macroprolactin levels in patients with moderate and severe renal failure (Stage 3, 4, and 5) according to the U.S. NKF-DOQI classification (p < 0.001). Prolactin and macroprolactin levels were not increased in patients with normoalbuminuria, microalbuminuria and macroalbuminuria (p > 0.05). Serum creatinine levels correleted positively with both prolactin (r = 0.51, p < 0.001) and macroprolactin levels (r = 0.43, p < 0.001). On the other hand, glomerular filtration rate correlated negatively with both prolactin (r = -0.54, p < 0.001) and macroprolactin levels (r = -0.44, p < 0.001). Albuminuria significantly related with neither prolactin nor macroprolactin levels (p > 0.05).

In the present study, we found that not only serum prolactin but also serum macroprolactin levels increased especially in moderate to severe renal failure which was due to decreased glomerular filtration and renal parenchymal function resulting in an increased amount of monomeric prolactin and macroprolactin in the circulation in patients with Type 2 diabetes mellitus.