Aldosterone increases the reabsorption of sodium and excretion of potassium in the kidneys. Thus, increased aldosterone secretion would lead to hypokalemia, not hyperkalemia.

Decreased activity of the sodium-potassium ATPase pump could lead to intracellular potassium accumulation, potentially leading to hyperkalemia. However, this is not the most likely explanation in this case.

Increased serum potassium concentration (hyperkalemia) is commonly due to decreased renal excretion. The kidneys play a key role in regulating the body's potassium levels, and any impairment in renal function can lead to potassium build-up in the bloodstream. In the case of the patient with chronic constipation, his lack of bowel movements is likely exacerbating this problem as the colon also plays a role in potassium homeostasis.

While excess dietary intake of potassium can contribute to hyperkalemia, the kidneys typically compensate by increasing potassium excretion. Therefore, unless the patient has kidney disease, it is unlikely for increased dietary intake alone to cause hyperkalemia.