Question

Given below are two statements:
Statement (I): In fish, prolactin increases glomerular filtration rate in the kidney
Statement (II): In fish, prolactin functions predominately in freshwater osmoregulation
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are true.
• B. Both Statement (I) and Statement (II) are false.
• C. Statement (I) is true but Statement (II) is false.
• D. Statement (I) is false but Statement (II) is true.

Hint:

Prolactin acts as a barrier hormone in freshwater fish, reducing permeability to water and promoting active ion retention, but does not increase GFR.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Osmoregulation in teleost fish is regulated by endocrine hormones. Prolactin (PRL) is a pituitary hormone that plays a major role in adaptation to freshwater.

Step 2: Detailed Explanation:
- Statement (I): In freshwater, teleost fish are hyperosmotic to their surroundings, meaning water constantly enters their bodies. To maintain balance, they must excrete excess water as dilute urine. Prolactin acts on the kidneys to decrease water permeability of the renal tubules and promote sodium and chloride reabsorption. However, research indicates that prolactin generally does not increase the glomerular filtration rate (GFR). Hormones like cortisol and thyroid hormones are typically responsible for increasing GFR, while prolactin works primarily to regulate tubular ion reabsorption and reduce GFR or keep it stable to prevent rapid fluid loss under certain conditions. Thus, Statement (I) is false.
- Statement (II): Prolactin is often called the "freshwater hormone" in fish physiology because it is required for survival in freshwater environments. It reduces permeability of the gills and urinary bladder to water and promotes active ion uptake. Thus, Statement (II) is true.

Step 3: Final Answer:
Therefore, Statement (I) is false, but Statement (II) is true.