Human seminal plasma contains somatostatin-64

Area of Science:

• Endocrinology
• Reproductive Biology
• Peptide Chemistry

Background:

• Prosomatostatin yields somatostatin (SS)-14 and SS-28, with distinct tissue distributions.
• SS-14 is widespread, while SS-28 is concentrated in the intestine.

Purpose of the Study:

• To investigate the identity and concentration of somatostatin-like immunoreactivity in human seminal plasma.
• To determine the potential origin of somatostatin peptides in seminal fluid.

Main Methods:

• Gel chromatography to determine molecular weight (M(r)) of SS in seminal plasma.
• N-terminal sequencing and mass spectrometry (m.s.) for SS-64 identification.
• Radioligand binding assays to assess SS-64's biological activity.
• Comparison of SS-64 levels in normal and vasectomized men.

Main Results:

• Human seminal plasma contains high concentrations of SS with an M(r) greater than SS-28.
• The isolated peptide was identified as SS-64, sharing N-terminal sequence and M(r) with a previously uncharacterized peptide.
• SS-64 demonstrated potent binding affinity to SS-14 receptors.
• Seminal plasma SS-64 concentrations were significantly higher in vasectomized men compared to normal men.

Conclusions:

• Human seminal plasma contains a novel somatostatin-64 peptide.
• SS-64 exhibits biological activity comparable to SS-14.
• The elevated levels in vasectomized individuals strongly suggest synthesis within the male accessory sex glands.