A defective pituitary gland in a black cat may result in the cat’s hair becoming red/brown because of the lack of production a hormone produced by the pituitary gland. One of these hormones makes a certain protein (MCR1) in the cells of the cat’s skin work. This protein is employed in the conversion of pheomelanin (yellow/red) to eumelanin (brown/black) pigment. If it is not working the pigment stays yellow/red. Hence rusty coloured hair.
Note: this is my own work. No one has written this before. Please check. It took about 90 minutes of vigorous online research. This page is a follow up to “Is your black cat rusty red?” and Julie’s comments on that page.
Expanded Summary: The pituitary gland is situated at the base of the brain. It produces eight hormones. Decreased production of these hormones is called: Hypopituitarism.
There is a protein, MC1R, that is within the cell membrane of the skin, which is signalled (fired into action) by a “melanocyte-stimulating” hormone (MSH) that is released by the pituitary gland.
When activated by MSH, MC1R initiates the production of the brown or black pigment eumelanin from pheomelanin, which is a yellow-red color pigment and the precursor to eumelanin (brown black). In short, yellow and red pigment molecules are chemically altered to become brown and black.
MC1R is a protein that is the switch that converts yellow red to brown black. If it is not fired into action due to pituitary gland malfunction the pigment in the hair strands remain yellow/red and not brown/black.
One of the reasons for a malfunctioning pituitary gland is congenital – genetically inherited health problem. Other reasons (selected) are as follows:
- Tumor
- Brain injury
- Infection
- Stroke
Note: There is a connection between the “cure” for rusty red black cats, the supplement tyrosine, and the thyroid gland which in turn is affected by the pituitary gland:
One of the hormones produced by the pituitary gland is the thyroid-stimulating hormone (“TSH”). A deficiency of this hormone leads to hypothyroidism. Hypothyroidism is a lack of production of thyroxine (T4) and triiodothyronine (T3). (Note: tyrosine is involved in the production of thyroid hormones).
Sources: these are numerous and include my own work and Wikipedia. The main work was about “connecting the dots”.
See how black, shiny black the rest of Katey is? All of them were that black in all light in years past. None of them are as rusty as Ziggy, yet, but I wonder if that’s where they’re heading. And I wonder if it’s a symptom of ill health, though these 3 are not exhibiting any other health abnormalities…
And this is Katey, the youngest. I see it starting on her head now.
It’s more obvious when she’s sitting in the sun here.
This is Bobbie. I just recently noticed that she’s changing color.
This is Spike, the one who’s been changing color the longest. It’s quite obvious around his shoulders.
Two points come to mind (and I am not an expert on this problem). The first point is probably obvious. Black cats are really dark brown because the pigment in the fur strands, eumelanin is dark brown. When light shines through it, it looks light brown/rusty. The coat color depends on the light.
Secondly, if the diet you are feeding to all three cats is deficient in tyrosine it would affect all the cats as you state — but you say it isn’t defecient in tyrosine. One other factor is age. Older black cats tend to go rusty. As to health a lack of tyrosine, I don’t think there are major or minor health issues. Lack of tyrosine is a symptom and the cause my be a serious health issue but a vet will answer that one.
Cushings disease has been linked (in comments) to the rusty coat and lack of tyrosine but I forget where the comment is. You may have seen the comment. Sorry I am not very precise but this is a bit of a mystery.
Thanks for posting Diane. Stick around. Do you have photos?