Parathyroid hormone-like immunoreactivity in fish plasma and tissues

Area of Science:

• Comparative Endocrinology
• Fish Physiology
• Hormone Research

Background:

• Fish lack parathyroid glands, the primary source of parathyroid hormone (PTH) in mammals.
• Previous studies indicated the presence of PTH-like substances in fish circulation.

Purpose of the Study:

• To investigate the potential sources of circulating parathyroid hormone (PTH)-like substances in fish.
• To characterize the immunoreactive (IR) PTH in various fish tissues.

Main Methods:

• Radioimmunoassays were used to detect and quantify immunoreactive (IR) PTH in plasma and tissue extracts (brain, pituitary, corpuscles of Stannius, muscle, liver, kidney) of trout and goldfish.
• Sep Pak column chromatography was employed to purify IR PTH from pituitary extracts.
• Heat treatment was used to assess the stability of IR PTH in different tissue extracts.

Main Results:

• Immunoreactive (IR) PTH was detected in the plasma of trout and goldfish.
• Higher concentrations of IR PTH were found in brain and pituitary extracts compared to plasma.
• IR PTH was also present in the corpuscles of Stannius (CS), with distinct characteristics from brain and pituitary IR PTH, particularly regarding heat sensitivity of N-terminal PTH.
• IR PTH was absent in muscle, liver, and kidney extracts.

Conclusions:

• The brain, pituitary gland, and corpuscles of Stannius (CS) in fish produce peptides that cross-react with antibodies against mammalian PTH.
• The IR PTH produced by the CS appears to differ from that of the brain and pituitary.
• These tissues are likely the source of circulating IR PTH in fish.