VIP and PHI in cat neurons: co-localization but variable tissue content possible due to differential processing

Area of Science:

• Neuroscience
• Endocrinology
• Gastroenterology

Background:

• Vasoactive intestinal polypeptide (VIP) and peptide histidine isoleucine (PHI) are neuropeptides with diverse physiological roles.
• The co-expression and differential distribution of VIP and PHI in the central and peripheral nervous systems are not fully understood.

Purpose of the Study:

• To compare the concentrations and immunohistochemical localization of VIP and PHI in various feline tissues.
• To investigate potential differences in their molecular forms and tissue-specific expression patterns.

Main Methods:

• Quantification of VIP and PHI concentrations using radioimmunoassay.
• Immunohistochemical analysis for peptide localization.
• Gel-permeation chromatography to identify molecular forms.

Main Results:

• VIP concentrations were significantly higher than PHI in the gastrointestinal tract, genitourinary tract, lung, and heart.
• In the neurohypophysis, the VIP/PHI ratio was approximately 1.
• Immunohistochemistry revealed co-localization of VIP and PHI in the same ganglion cells in the intestine, pancreas, uterus, and sympathetic ganglia.
• Larger molecular forms of VIP and PHI, potentially representing precursors, were detected in the intestine, pancreas, and brain.
• The median eminence and posterior pituitary showed higher PHI than VIP immunoreactivity.

Conclusions:

• VIP and PHI coexist in most neuronal systems in cats.
• While the precursor gene ratio is 1:1, posttranslational processing differences result in higher VIP content in many terminal areas.
• Tissue-specific processing of VIP and PHI influences their final concentrations and distribution.