Golden Hamster Pancreatic Islets: A Tissue Rich in Monoamine Oxidase*

Abstract

We compared the steady state monoamine oxidase (MAO) activity of collagenase-isolated pancreatic islets of the golden hamster with the steady state MAO activity of liver, kidney, median eminence, pituitary, acinar pancreas, and cerebral cortex. The MAO activity of the islets (5384 +/- 412 pmol/mg protein . min) was 3-fold greater than the activity of the next highest tissue (liver) and 12.5 times greater than the activity of the acinar pancreas. This high MAO activity was not due to collagenase exposure. The islet MAO was mainly of the so-called type B, although there was also some type A activity in this tissue. By assaying the formation of new islet MAO after the irreversible activation of MAO by the MAO inhibitor pargyline, we found that the t 1/2 of islet MAO (5.9 days with 95% confidence limits of 4.1-10.5 days) did not differ from the t 1/2 of MAO in tissues with lower steady state MAO activities. This suggested that the high steady state MAO activity in golden hamster islets is due to a high rate of synthesis rather than to a lower rate of degradation. Although rats, Chinese hamsters, guinea pigs, mice, and rabbits had substantial MAO activity in their pancreatic islets, their levels, at most, were only 16% that of the golden hamster. When the MAO activity of golden hamster islets was inhibited by the administration of pargyline plus clorgyline, there was a 3-fold increase in islet serotonin concentration, with no increase in islet norepinephrine concentration, suggesting that islet MAO activity plays a role in regulating islet serotonin concentration.

Blood‐Brain Barrier Monoamine Oxidase: Enzyme Characterization in Cerebral Microvessels and Other Tissues from Six Mammalian Species, Including Human

“…Our results showed that the half-life of MAO-B was 8-9 days, whereas that of MAO-A was longer (results not shown). These results are consistent with the previous findings of Feldman et al (1980).…”

“…Since the properties of M A 0 from brain microvessels and cortical P2 preparations are similar, taking into account the presence of both molecular forms, it is possible that the turnover of M A 0 in microvessels reflects overall brain endothelial cell turnover, rather than of M A 0 itself. However, previous results showed that the half-life of M A 0 from different brain regions in rats (Goridis and Neff, 1971) and M A 0 from peripheral organs like the islets of Langerhans and brain of the hamster (Feldman et al, 1980) were similar. Whether the differences in M A 0 turnover in microvessels and cortex are due to differences in M A 0 protein and/or mitochondria is uncertain.…”

Resistance of Golden Hamster to l‐Methyl‐4‐Phenyl‐1,2,3,6 Tetrahydropyridine: Relationship with Low Levels of Regional Monoamine Oxidase B

“…Studies on MA0 in mouse strains other than BALB/c are innumerable in the literature (Squires, 1972;Heikkila et al, 1985;Melamed et al, 1985;Zimmer and Geneser, 1987) and such studies in GH are limited to a couple of reports (Edwards and Malsbury, 1978;Feldman et al, 1980). Their studies, though clearly demonstrating a significant lack of MA0 B type in GH brain, are either limited to the whole brain crude homogenate or are restricted to cerebral cortex.…”

Neurofunctional imaging of β‐cell dynamics

“…Since then, it has become clear that not only β‐cells do contain monoamine neurotransmitters but also that most if not all of the enzymes needed for de novo synthesis and catabolism of monoamines, including: tyrosine hydroxylase (TH), the enzyme catalysing the rate‐limiting synthetic step whereby tyrosine is converted to l ‐DOPA ; l ‐DOPA decarboxylase (a.k.a. aromatic l ‐amino acid decarboxylase (AADC) producing DA; the catabolic enzymes acting on DA, monoamine oxidase (MAO‐B) , AADC and catechol‐ O ‐methyl transferase . Recently, the gene expression pattern needed for encoding all of the products necessary for synthesizing, packaging and secreting serotonin, including both isoforms of the serotonin synthetic enzyme tryptophan hydroxylase, has been found in islets .…”